782 lines
29 KiB
Text
782 lines
29 KiB
Text
-- Copyright (c) 2014 Floris van Doorn. All rights reserved.
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-- Released under Apache 2.0 license as described in the file LICENSE.
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-- Authors: Floris van Doorn, Jeremy Avigad
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-- int.basic
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-- =========
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-- The integers, with addition, multiplication, and subtraction.
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import ..nat.basic ..nat.order ..nat.sub ..prod ..quotient ..quotient tools.tactic struc.relation
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import struc.binary
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import tools.fake_simplifier
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open nat (hiding case)
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open quotient subtype prod relation
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open decidable binary fake_simplifier
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open eq_ops
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namespace int
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-- ## The defining equivalence relation on ℕ × ℕ
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abbreviation rel (a b : ℕ × ℕ) : Prop := pr1 a + pr2 b = pr2 a + pr1 b
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theorem rel_comp (n m k l : ℕ) : (rel (pair n m) (pair k l)) ↔ (n + l = m + k) :=
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have H : (pr1 (pair n m) + pr2 (pair k l) = pr2 (pair n m) + pr1 (pair k l)) ↔ (n + l = m + k),
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by simp,
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H
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-- add_rewrite rel_comp --local
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theorem rel_refl {a : ℕ × ℕ} : rel a a :=
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add_comm
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theorem rel_symm {a b : ℕ × ℕ} (H : rel a b) : rel b a :=
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calc
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pr1 b + pr2 a = pr2 a + pr1 b : add_comm
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... = pr1 a + pr2 b : H⁻¹
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... = pr2 b + pr1 a : add_comm
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theorem rel_trans {a b c : ℕ × ℕ} (H1 : rel a b) (H2 : rel b c) : rel a c :=
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have H3 : pr1 a + pr2 c + pr2 b = pr2 a + pr1 c + pr2 b, from
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calc
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pr1 a + pr2 c + pr2 b = pr1 a + pr2 b + pr2 c : by simp
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... = pr2 a + pr1 b + pr2 c : {H1}
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... = pr2 a + (pr1 b + pr2 c) : by simp
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... = pr2 a + (pr2 b + pr1 c) : {H2}
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... = pr2 a + pr1 c + pr2 b : by simp,
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show pr1 a + pr2 c = pr2 a + pr1 c, from add_cancel_right H3
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theorem rel_equiv : is_equivalence rel :=
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is_equivalence_mk
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(is_reflexive_mk @rel_refl)
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(is_symmetric_mk @rel_symm)
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(is_transitive_mk @rel_trans)
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theorem rel_flip {a b : ℕ × ℕ} (H : rel a b) : rel (flip a) (flip b) :=
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calc
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pr1 (flip a) + pr2 (flip b) = pr2 a + pr1 b : by simp
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... = pr1 a + pr2 b : H⁻¹
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... = pr2 (flip a) + pr1 (flip b) : by simp
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-- ## The canonical representative of each equivalence class
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definition proj (a : ℕ × ℕ) : ℕ × ℕ :=
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if pr1 a ≥ pr2 a then pair (pr1 a - pr2 a) 0 else pair 0 (pr2 a - pr1 a)
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theorem proj_ge {a : ℕ × ℕ} (H : pr1 a ≥ pr2 a) : proj a = pair (pr1 a - pr2 a) 0 :=
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if_pos H
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theorem proj_lt {a : ℕ × ℕ} (H : pr1 a < pr2 a) : proj a = pair 0 (pr2 a - pr1 a) :=
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have H2 : ¬ pr1 a ≥ pr2 a, from lt_imp_not_ge H,
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if_neg H2
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theorem proj_le {a : ℕ × ℕ} (H : pr1 a ≤ pr2 a) : proj a = pair 0 (pr2 a - pr1 a) :=
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or_elim le_or_gt
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(assume H2 : pr2 a ≤ pr1 a,
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have H3 : pr1 a = pr2 a, from le_antisym H H2,
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calc
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proj a = pair (pr1 a - pr2 a) 0 : proj_ge H2
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... = pair (pr1 a - pr2 a) (pr1 a - pr1 a) : {sub_self⁻¹}
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... = pair (pr2 a - pr2 a) (pr2 a - pr1 a) : {H3}
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... = pair 0 (pr2 a - pr1 a) : {sub_self})
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(assume H2 : pr1 a < pr2 a, proj_lt H2)
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theorem proj_ge_pr1 {a : ℕ × ℕ} (H : pr1 a ≥ pr2 a) : pr1 (proj a) = pr1 a - pr2 a :=
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calc
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pr1 (proj a) = pr1 (pair (pr1 a - pr2 a) 0) : {proj_ge H}
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... = pr1 a - pr2 a : pr1_pair (pr1 a - pr2 a) 0
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theorem proj_ge_pr2 {a : ℕ × ℕ} (H : pr1 a ≥ pr2 a) : pr2 (proj a) = 0 :=
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calc
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pr2 (proj a) = pr2 (pair (pr1 a - pr2 a) 0) : {proj_ge H}
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... = 0 : pr2_pair (pr1 a - pr2 a) 0
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theorem proj_le_pr1 {a : ℕ × ℕ} (H : pr1 a ≤ pr2 a) : pr1 (proj a) = 0 :=
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calc
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pr1 (proj a) = pr1 (pair 0 (pr2 a - pr1 a)) : {proj_le H}
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... = 0 : pr1_pair 0 (pr2 a - pr1 a)
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theorem proj_le_pr2 {a : ℕ × ℕ} (H : pr1 a ≤ pr2 a) : pr2 (proj a) = pr2 a - pr1 a :=
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calc
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pr2 (proj a) = pr2 (pair 0 (pr2 a - pr1 a)) : {proj_le H}
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... = pr2 a - pr1 a : pr2_pair 0 (pr2 a - pr1 a)
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theorem proj_flip (a : ℕ × ℕ) : proj (flip a) = flip (proj a) :=
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have special : ∀a, pr2 a ≤ pr1 a → proj (flip a) = flip (proj a), from
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take a,
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assume H : pr2 a ≤ pr1 a,
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have H2 : pr1 (flip a) ≤ pr2 (flip a), from P_flip H,
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have H3 : pr1 (proj (flip a)) = pr1 (flip (proj a)), from
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calc
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pr1 (proj (flip a)) = 0 : proj_le_pr1 H2
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... = pr2 (proj a) : symm (proj_ge_pr2 H)
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... = pr1 (flip (proj a)) : symm (flip_pr1 (proj a)),
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have H4 : pr2 (proj (flip a)) = pr2 (flip (proj a)), from
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calc
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pr2 (proj (flip a)) = pr2 (flip a) - pr1 (flip a) : proj_le_pr2 H2
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... = pr1 a - pr1 (flip a) : {flip_pr2 a}
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... = pr1 a - pr2 a : {flip_pr1 a}
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... = pr1 (proj a) : (proj_ge_pr1 H)⁻¹
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... = pr2 (flip (proj a)) : (flip_pr2 (proj a))⁻¹,
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prod_eq H3 H4,
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or_elim le_total
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(assume H : pr2 a ≤ pr1 a, special a H)
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(assume H : pr1 a ≤ pr2 a,
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have H2 : pr2 (flip a) ≤ pr1 (flip a), from P_flip H,
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calc
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proj (flip a) = flip (flip (proj (flip a))) : symm (flip_flip (proj (flip a)))
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... = flip (proj (flip (flip a))) : {symm (special (flip a) H2)}
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... = flip (proj a) : {flip_flip a})
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theorem proj_rel (a : ℕ × ℕ) : rel a (proj a) :=
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or_elim le_total
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(assume H : pr2 a ≤ pr1 a,
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calc
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pr1 a + pr2 (proj a) = pr1 a + 0 : {proj_ge_pr2 H}
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... = pr1 a : add_zero_right
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... = pr2 a + (pr1 a - pr2 a) : (add_sub_le H)⁻¹
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... = pr2 a + pr1 (proj a) : {(proj_ge_pr1 H)⁻¹})
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(assume H : pr1 a ≤ pr2 a,
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calc
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pr1 a + pr2 (proj a) = pr1 a + (pr2 a - pr1 a) : {proj_le_pr2 H}
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... = pr2 a : add_sub_le H
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... = pr2 a + 0 : add_zero_right⁻¹
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... = pr2 a + pr1 (proj a) : {(proj_le_pr1 H)⁻¹})
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theorem proj_congr {a b : ℕ × ℕ} (H : rel a b) : proj a = proj b :=
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have special : ∀a b, pr2 a ≤ pr1 a → rel a b → proj a = proj b, from
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take a b,
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assume H2 : pr2 a ≤ pr1 a,
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assume H : rel a b,
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have H3 : pr1 a + pr2 b ≤ pr2 a + pr1 b, from H ▸ le_refl,
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have H4 : pr2 b ≤ pr1 b, from add_le_inv H3 H2,
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have H5 : pr1 (proj a) = pr1 (proj b), from
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calc
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pr1 (proj a) = pr1 a - pr2 a : proj_ge_pr1 H2
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... = pr1 a + pr2 b - pr2 b - pr2 a : {sub_add_left⁻¹}
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... = pr2 a + pr1 b - pr2 b - pr2 a : {H}
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... = pr2 a + pr1 b - pr2 a - pr2 b : {sub_comm}
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... = pr1 b - pr2 b : {sub_add_left2}
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... = pr1 (proj b) : (proj_ge_pr1 H4)⁻¹,
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have H6 : pr2 (proj a) = pr2 (proj b), from
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calc
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pr2 (proj a) = 0 : proj_ge_pr2 H2
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... = pr2 (proj b) : {symm (proj_ge_pr2 H4)},
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prod_eq H5 H6,
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or_elim le_total
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(assume H2 : pr2 a ≤ pr1 a, special a b H2 H)
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(assume H2 : pr1 a ≤ pr2 a,
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have H3 : pr2 (flip a) ≤ pr1 (flip a), from P_flip H2,
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have H4 : proj (flip a) = proj (flip b), from special (flip a) (flip b) H3 (rel_flip H),
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have H5 : flip (proj a) = flip (proj b), from proj_flip a ▸ proj_flip b ▸ H4,
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show proj a = proj b, from flip_inj H5)
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theorem proj_inj {a b : ℕ × ℕ} (H : proj a = proj b) : rel a b :=
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representative_map_equiv_inj rel_equiv proj_rel @proj_congr H
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theorem proj_zero_or (a : ℕ × ℕ) : pr1 (proj a) = 0 ∨ pr2 (proj a) = 0 :=
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or_elim le_total
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(assume H : pr2 a ≤ pr1 a, or_inr (proj_ge_pr2 H))
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(assume H : pr1 a ≤ pr2 a, or_inl (proj_le_pr1 H))
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theorem proj_idempotent (a : ℕ × ℕ) : proj (proj a) = proj a :=
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representative_map_idempotent_equiv proj_rel @proj_congr a
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-- ## Definition of ℤ and basic theorems and definitions
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definition int := image proj
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notation `ℤ` := int
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definition psub : ℕ × ℕ → ℤ := fun_image proj
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definition rep : ℤ → ℕ × ℕ := subtype.elt_of
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theorem quotient : is_quotient rel psub rep :=
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representative_map_to_quotient_equiv rel_equiv proj_rel @proj_congr
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theorem psub_rep (a : ℤ) : psub (rep a) = a :=
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abs_rep quotient a
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theorem destruct (a : ℤ) : ∃n m : ℕ, a = psub (pair n m) :=
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exists_intro (pr1 (rep a))
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(exists_intro (pr2 (rep a))
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(calc
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a = psub (rep a) : symm (psub_rep a)
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... = psub (pair (pr1 (rep a)) (pr2 (rep a))) : {symm (prod_ext (rep a))}))
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definition of_nat (n : ℕ) : ℤ := psub (pair n 0)
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theorem int_eq_decidable [instance] (a b : ℤ) : decidable (a = b) := _
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-- subtype_eq_decidable _ _ (prod_eq_decidable _ _ _ _)
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opaque_hint (hiding int)
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coercion of_nat
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theorem eq_zero_intro (n : ℕ) : psub (pair n n) = 0 :=
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have H : rel (pair n n) (pair 0 0), by simp,
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eq_abs quotient H
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definition to_nat : ℤ → ℕ := rec_constant quotient (fun v, dist (pr1 v) (pr2 v))
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theorem to_nat_comp (n m : ℕ) : (to_nat (psub (pair n m))) = dist n m :=
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have H : ∀v w : ℕ × ℕ, rel v w → dist (pr1 v) (pr2 v) = dist (pr1 w) (pr2 w),
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from take v w H, dist_eq_intro H,
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have H2 : ∀v : ℕ × ℕ, (to_nat (psub v)) = dist (pr1 v) (pr2 v),
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from take v, (comp_constant quotient H rel_refl),
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iff_mp (by simp) H2 (pair n m)
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-- add_rewrite to_nat_comp --local
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theorem to_nat_of_nat (n : ℕ) : to_nat (of_nat n) = n :=
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calc
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(to_nat (psub (pair n 0))) = dist n 0 : by simp
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... = n : by simp
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theorem of_nat_inj {n m : ℕ} (H : of_nat n = of_nat m) : n = m :=
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calc
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n = to_nat (of_nat n) : symm (to_nat_of_nat n)
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... = to_nat (of_nat m) : {H}
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... = m : to_nat_of_nat m
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theorem to_nat_eq_zero {a : ℤ} (H : to_nat a = 0) : a = 0 :=
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obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
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have H2 : dist xa ya = 0, from
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calc
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dist xa ya = (to_nat (psub (pair xa ya))) : by simp
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... = (to_nat a) : {symm Ha}
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... = 0 : H,
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have H3 : xa = ya, from dist_eq_zero H2,
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calc
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a = psub (pair xa ya) : Ha
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... = psub (pair ya ya) : {H3}
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... = 0 : eq_zero_intro ya
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-- add_rewrite to_nat_of_nat
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-- ## neg
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definition neg : ℤ → ℤ := quotient_map quotient flip
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-- TODO: is this good? Note: replacing 100 by max makes it bind stronger than application.
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notation `-` x:100 := neg x
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theorem neg_comp (n m : ℕ) : -(psub (pair n m)) = psub (pair m n) :=
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have H : ∀a, -(psub a) = psub (flip a),
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from take a, comp_quotient_map quotient @rel_flip rel_refl,
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calc
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-(psub (pair n m)) = psub (flip (pair n m)) : H (pair n m)
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... = psub (pair m n) : by simp
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-- add_rewrite neg_comp --local
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theorem neg_zero : -0 = 0 :=
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calc -(psub (pair 0 0)) = psub (pair 0 0) : neg_comp 0 0
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theorem neg_neg (a : ℤ) : -(-a) = a :=
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obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
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by simp
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-- add_rewrite neg_neg neg_zero
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theorem neg_inj {a b : ℤ} (H : -a = -b) : a = b :=
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iff_mp (by simp) (congr_arg neg H)
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theorem neg_move {a b : ℤ} (H : -a = b) : -b = a :=
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subst H (neg_neg a)
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theorem to_nat_neg (a : ℤ) : (to_nat (-a)) = (to_nat a) :=
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obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
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by simp
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theorem pos_eq_neg {n m : ℕ} (H : n = -m) : n = 0 ∧ m = 0 :=
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have H2 : ∀n : ℕ, n = psub (pair n 0), from take n : ℕ, refl (n),
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have H3 : psub (pair n 0) = psub (pair 0 m), from iff_mp (by simp) H,
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have H4 : rel (pair n 0) (pair 0 m), from R_intro_refl quotient @rel_refl H3,
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have H5 : n + m = 0, from
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calc
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n + m = pr1 (pair n 0) + pr2 (pair 0 m) : by simp
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... = pr2 (pair n 0) + pr1 (pair 0 m) : H4
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... = 0 : by simp,
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add_eq_zero H5
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-- add_rewrite to_nat_neg
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---reverse equalities
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opaque_hint (exposing int)
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theorem cases (a : ℤ) : (∃n : ℕ, a = of_nat n) ∨ (∃n : ℕ, a = - n) :=
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have Hrep : proj (rep a) = rep a, from @idempotent_image_fix _ proj proj_idempotent a,
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or_imp_or (or_swap (proj_zero_or (rep a)))
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(assume H : pr2 (proj (rep a)) = 0,
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have H2 : pr2 (rep a) = 0, from subst Hrep H,
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exists_intro (pr1 (rep a))
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(calc
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a = psub (rep a) : symm (psub_rep a)
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... = psub (pair (pr1 (rep a)) (pr2 (rep a))) : {symm (prod_ext (rep a))}
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... = psub (pair (pr1 (rep a)) 0) : {H2}
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... = of_nat (pr1 (rep a)) : refl _))
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(assume H : pr1 (proj (rep a)) = 0,
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have H2 : pr1 (rep a) = 0, from subst Hrep H,
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exists_intro (pr2 (rep a))
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(calc
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a = psub (rep a) : symm (psub_rep a)
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... = psub (pair (pr1 (rep a)) (pr2 (rep a))) : {symm (prod_ext (rep a))}
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... = psub (pair 0 (pr2 (rep a))) : {H2}
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... = -(psub (pair (pr2 (rep a)) 0)) : by simp
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... = -(of_nat (pr2 (rep a))) : refl _))
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opaque_hint (hiding int)
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---rename to by_cases in Lean 0.2 (for now using this to avoid name clash)
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theorem int_by_cases {P : ℤ → Prop} (a : ℤ) (H1 : ∀n : ℕ, P (of_nat n)) (H2 : ∀n : ℕ, P (-n)) :
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P a :=
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or_elim (cases a)
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(assume H, obtain (n : ℕ) (H3 : a = n), from H, subst (symm H3) (H1 n))
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(assume H, obtain (n : ℕ) (H3 : a = -n), from H, subst (symm H3) (H2 n))
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---reverse equalities, rename
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theorem cases_succ (a : ℤ) : (∃n : ℕ, a = of_nat n) ∨ (∃n : ℕ, a = - (of_nat (succ n))) :=
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or_elim (cases a)
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(assume H : (∃n : ℕ, a = of_nat n), or_inl H)
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(assume H,
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obtain (n : ℕ) (H2 : a = -(of_nat n)), from H,
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discriminate
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(assume H3 : n = 0,
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have H4 : a = of_nat 0, from
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calc
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a = -(of_nat n) : H2
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... = -(of_nat 0) : {H3}
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... = of_nat 0 : neg_zero,
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or_inl (exists_intro 0 H4))
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(take k : ℕ,
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assume H3 : n = succ k,
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have H4 : a = -(of_nat (succ k)), from subst H3 H2,
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or_inr (exists_intro k H4)))
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theorem int_by_cases_succ {P : ℤ → Prop} (a : ℤ)
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(H1 : ∀n : ℕ, P (of_nat n)) (H2 : ∀n : ℕ, P (-(of_nat (succ n)))) : P a :=
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or_elim (cases_succ a)
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(assume H, obtain (n : ℕ) (H3 : a = of_nat n), from H, subst (symm H3) (H1 n))
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(assume H, obtain (n : ℕ) (H3 : a = -(of_nat (succ n))), from H, subst (symm H3) (H2 n))
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theorem of_nat_eq_neg_of_nat {n m : ℕ} (H : n = - m) : n = 0 ∧ m = 0 :=
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have H2 : n = psub (pair 0 m), from
|
||
calc
|
||
n = -m : H
|
||
... = -(psub (pair m 0)) : refl (-m)
|
||
... = psub (pair 0 m) : by simp,
|
||
have H3 : rel (pair n 0) (pair 0 m), from R_intro_refl quotient @rel_refl H2,
|
||
have H4 : n + m = 0, from
|
||
calc
|
||
n + m = pr1 (pair n 0) + pr2 (pair 0 m) : by simp
|
||
... = pr2 (pair n 0) + pr1 (pair 0 m) : H3
|
||
... = 0 : by simp,
|
||
add_eq_zero H4
|
||
|
||
--some of these had to be transparent for theorem cases
|
||
opaque_hint (hiding psub proj)
|
||
|
||
-- ## add
|
||
|
||
theorem rel_add {a a' b b' : ℕ × ℕ} (Ha : rel a a') (Hb : rel b b')
|
||
: rel (map_pair2 add a b) (map_pair2 add a' b') :=
|
||
calc
|
||
pr1 (map_pair2 add a b) + pr2 (map_pair2 add a' b') = pr1 a + pr2 a' + (pr1 b + pr2 b') : by simp
|
||
... = pr2 a + pr1 a' + (pr1 b + pr2 b') : {Ha}
|
||
... = pr2 a + pr1 a' + (pr2 b + pr1 b') : {Hb}
|
||
... = pr2 (map_pair2 add a b) + pr1 (map_pair2 add a' b') : by simp
|
||
|
||
definition add : ℤ → ℤ → ℤ := quotient_map_binary quotient (map_pair2 nat.add)
|
||
infixl `+` := int.add
|
||
|
||
theorem add_comp (n m k l : ℕ) : psub (pair n m) + psub (pair k l) = psub (pair (n + k) (m + l)) :=
|
||
have H : ∀a b, psub a + psub b = psub (map_pair2 nat.add a b),
|
||
from comp_quotient_map_binary_refl @rel_refl quotient @rel_add,
|
||
H (pair n m) (pair k l) ⬝ by simp
|
||
|
||
-- add_rewrite add_comp --local
|
||
|
||
theorem add_comm (a b : ℤ) : a + b = b + a :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
by simp
|
||
|
||
theorem add_assoc (a b c : ℤ) : a + b + c = a + (b + c) :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
obtain (xc yc : ℕ) (Hc : c = psub (pair xc yc)), from destruct c,
|
||
by simp
|
||
|
||
theorem add_left_comm (a b c : ℤ) : a + (b + c) = b + (a + c) :=
|
||
left_comm add_comm add_assoc a b c
|
||
|
||
theorem add_right_comm (a b c : ℤ) : a + b + c = a + c + b :=
|
||
right_comm add_comm add_assoc a b c
|
||
|
||
-- ### interaction of add with other functions and constants
|
||
|
||
theorem add_zero_right (a : ℤ) : a + 0 = a :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
have H0 : 0 = psub (pair 0 0), from refl 0,
|
||
by simp
|
||
|
||
theorem add_zero_left (a : ℤ) : 0 + a = a :=
|
||
subst (add_comm a 0) (add_zero_right a)
|
||
|
||
theorem add_inverse_right (a : ℤ) : a + -a = 0 :=
|
||
have H : ∀n, psub (pair n n) = 0, from eq_zero_intro,
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
by simp
|
||
|
||
theorem add_inverse_left (a : ℤ) : -a + a = 0 :=
|
||
subst (add_comm a (-a)) (add_inverse_right a)
|
||
|
||
theorem neg_add_distr (a b : ℤ) : -(a + b) = -a + -b :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
by simp
|
||
|
||
theorem to_nat_add_le (a b : ℤ) : to_nat (a + b) ≤ to_nat a + to_nat b :=
|
||
--note: ≤ is nat::≤
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
have H : dist (xa + xb) (ya + yb) ≤ dist xa ya + dist xb yb,
|
||
from dist_add_le_add_dist,
|
||
by simp
|
||
|
||
-- TODO: note, we have to add #nat to get the right interpretation
|
||
theorem add_of_nat (n m : nat) : of_nat n + of_nat m = #nat n + m := -- this is of_nat (n + m)
|
||
have H : ∀n : ℕ, n = psub (pair n 0), from take n : ℕ, refl n,
|
||
by simp
|
||
|
||
-- add_rewrite add_of_nat
|
||
|
||
theorem of_nat_succ (n : ℕ) : of_nat (succ n) = of_nat n + 1 :=
|
||
by simp
|
||
|
||
-- ## sub
|
||
definition sub (a b : ℤ) : ℤ := a + -b
|
||
infixl `-` := int.sub
|
||
|
||
theorem sub_def (a b : ℤ) : a - b = a + -b :=
|
||
refl (a - b)
|
||
|
||
theorem add_neg_right (a b : ℤ) : a + -b = a - b :=
|
||
refl (a - b)
|
||
|
||
theorem add_neg_left (a b : ℤ) : -a + b = b - a :=
|
||
add_comm (-a) b
|
||
|
||
-- opaque_hint (hiding int.sub)
|
||
|
||
theorem sub_neg_right (a b : ℤ) : a - (-b) = a + b :=
|
||
subst (neg_neg b) (refl (a - (-b)))
|
||
|
||
theorem sub_neg_neg (a b : ℤ) : -a - (-b) = b - a :=
|
||
subst (neg_neg b) (add_comm (-a) (-(-b)))
|
||
|
||
theorem sub_self (a : ℤ) : a - a = 0 :=
|
||
add_inverse_right a
|
||
|
||
theorem sub_zero_right (a : ℤ) : a - 0 = a :=
|
||
subst (symm neg_zero) (add_zero_right a)
|
||
|
||
theorem sub_zero_left (a : ℤ) : 0 - a = -a :=
|
||
add_zero_left (-a)
|
||
|
||
theorem neg_sub (a b : ℤ) : -(a - b) = -a + b :=
|
||
calc
|
||
-(a - b) = -a + -(-b) : neg_add_distr a (-b)
|
||
... = -a + b : {neg_neg b}
|
||
|
||
theorem neg_sub_flip (a b : ℤ) : -(a - b) = b - a :=
|
||
calc
|
||
-(a - b) = -a + b : neg_sub a b
|
||
... = b - a : add_comm (-a) b
|
||
|
||
theorem sub_sub_assoc (a b c : ℤ) : a - b - c = a - (b + c) :=
|
||
calc
|
||
a - b - c = a + (-b + -c) : add_assoc a (-b) (-c)
|
||
... = a + -(b + c) : {symm (neg_add_distr b c)}
|
||
|
||
theorem sub_add_assoc (a b c : ℤ) : a - b + c = a - (b - c) :=
|
||
calc
|
||
a - b + c = a + (-b + c) : add_assoc a (-b) c
|
||
... = a + -(b - c) : {symm (neg_sub b c)}
|
||
|
||
theorem add_sub_assoc (a b c : ℤ) : a + b - c = a + (b - c) :=
|
||
add_assoc a b (-c)
|
||
|
||
theorem add_sub_inverse (a b : ℤ) : a + b - b = a :=
|
||
calc
|
||
a + b - b = a + (b - b) : add_assoc a b (-b)
|
||
... = a + 0 : {sub_self b}
|
||
... = a : add_zero_right a
|
||
|
||
theorem add_sub_inverse2 (a b : ℤ) : a + b - a = b :=
|
||
subst (add_comm b a) (add_sub_inverse b a)
|
||
|
||
theorem sub_add_inverse (a b : ℤ) : a - b + b = a :=
|
||
subst (add_right_comm a b (-b)) (add_sub_inverse a b)
|
||
|
||
-- add_rewrite add_zero_left add_zero_right
|
||
-- add_rewrite add_comm add_assoc add_left_comm
|
||
-- add_rewrite sub_def add_inverse_right add_inverse_left
|
||
-- add_rewrite neg_add_distr
|
||
---- add_rewrite sub_sub_assoc sub_add_assoc add_sub_assoc
|
||
---- add_rewrite add_neg_right add_neg_left
|
||
---- add_rewrite sub_self
|
||
|
||
-- ### inversion theorems for add and sub
|
||
|
||
-- a + a = 0 -> a = 0
|
||
-- a = -a -> a = 0
|
||
|
||
theorem add_cancel_right {a b c : ℤ} (H : a + c = b + c) : a = b :=
|
||
calc
|
||
a = a + c - c : symm (add_sub_inverse a c)
|
||
... = b + c - c : {H}
|
||
... = b : add_sub_inverse b c
|
||
|
||
theorem add_cancel_left {a b c : ℤ} (H : a + b = a + c) : b = c :=
|
||
add_cancel_right (subst (subst H (add_comm a b)) (add_comm a c))
|
||
|
||
theorem add_eq_zero_right {a b : ℤ} (H : a + b = 0) : -a = b :=
|
||
have H2 : a + -a = a + b, from subst (symm (add_inverse_right a)) (symm H),
|
||
show -a = b, from add_cancel_left H2
|
||
|
||
theorem add_eq_zero_left {a b : ℤ} (H : a + b = 0) : -b = a :=
|
||
neg_move (add_eq_zero_right H)
|
||
|
||
theorem add_eq_self {a b : ℤ} (H : a + b = a) : b = 0 :=
|
||
add_cancel_left (trans H (symm (add_zero_right a)))
|
||
|
||
theorem sub_inj_left {a b c : ℤ} (H : a - b = a - c) : b = c :=
|
||
neg_inj (add_cancel_left H)
|
||
|
||
theorem sub_inj_right {a b c : ℤ} (H : a - b = c - b) : a = c :=
|
||
add_cancel_right H
|
||
|
||
theorem sub_eq_zero {a b : ℤ} (H : a - b = 0) : a = b :=
|
||
neg_inj (add_eq_zero_right H)
|
||
|
||
theorem add_imp_sub_right {a b c : ℤ} (H : a + b = c) : c - b = a :=
|
||
have H2 : c - b + b = a + b, from trans (sub_add_inverse c b) (symm H),
|
||
add_cancel_right H2
|
||
|
||
theorem add_imp_sub_left {a b c : ℤ} (H : a + b = c) : c - a = b :=
|
||
add_imp_sub_right (subst (add_comm a b) H)
|
||
|
||
theorem sub_imp_add {a b c : ℤ} (H : a - b = c) : c + b = a :=
|
||
subst (neg_neg b) (add_imp_sub_right H)
|
||
|
||
theorem sub_imp_sub {a b c : ℤ} (H : a - b = c) : a - c = b :=
|
||
have H2 : c + b = a, from sub_imp_add H, add_imp_sub_left H2
|
||
|
||
theorem sub_add_add_right (a b c : ℤ) : a + c - (b + c) = a - b :=
|
||
calc
|
||
a + c - (b + c) = a + (c - (b + c)) : add_sub_assoc a c (b + c)
|
||
... = a + (c - b - c) : {symm (sub_sub_assoc c b c)}
|
||
... = a + -b : {add_sub_inverse2 c (-b)}
|
||
|
||
theorem sub_add_add_left (a b c : ℤ) : c + a - (c + b) = a - b :=
|
||
subst (add_comm b c) (subst (add_comm a c) (sub_add_add_right a b c))
|
||
|
||
-- TODO: fix this
|
||
theorem dist_def (n m : ℕ) : dist n m = (to_nat (of_nat n - m)) :=
|
||
have H : of_nat n - m = psub (pair n m), from
|
||
calc
|
||
psub (pair n 0) + -psub (pair m 0) = psub (pair (n + 0) (0 + m)) : by simp
|
||
... = psub (pair n m) : by simp,
|
||
calc
|
||
dist n m = (to_nat (psub (pair n m))) : by simp
|
||
... = (to_nat (of_nat n - m)) : sorry -- {symm H}
|
||
|
||
-- ## mul
|
||
theorem rel_mul_prep {xa ya xb yb xn yn xm ym : ℕ}
|
||
(H1 : xa + yb = ya + xb) (H2 : xn + ym = yn + xm)
|
||
: xa * xn + ya * yn + (xb * ym + yb * xm) = xa * yn + ya * xn + (xb * xm + yb * ym) :=
|
||
have H3 : xa * xn + ya * yn + (xb * ym + yb * xm) + (yb * xn + xb * yn + (xb * xn + yb * yn))
|
||
= xa * yn + ya * xn + (xb * xm + yb * ym) + (yb * xn + xb * yn + (xb * xn + yb * yn)), from
|
||
calc
|
||
xa * xn + ya * yn + (xb * ym + yb * xm) + (yb * xn + xb * yn + (xb * xn + yb * yn))
|
||
= xa * xn + yb * xn + (ya * yn + xb * yn) + (xb * xn + xb * ym + (yb * yn + yb * xm))
|
||
: by simp
|
||
... = (xa + yb) * xn + (ya + xb) * yn + (xb * (xn + ym) + yb * (yn + xm)) : by simp
|
||
... = (ya + xb) * xn + (xa + yb) * yn + (xb * (yn + xm) + yb * (xn + ym)) : by simp
|
||
... = ya * xn + xb * xn + (xa * yn + yb * yn) + (xb * yn + xb * xm + (yb*xn + yb*ym))
|
||
: by simp
|
||
... = xa * yn + ya * xn + (xb * xm + yb * ym) + (yb * xn + xb * yn + (xb * xn + yb * yn))
|
||
: by simp,
|
||
nat.add_cancel_right H3
|
||
|
||
theorem rel_mul {u u' v v' : ℕ × ℕ} (H1 : rel u u') (H2 : rel v v') :
|
||
rel (pair (pr1 u * pr1 v + pr2 u * pr2 v) (pr1 u * pr2 v + pr2 u * pr1 v))
|
||
(pair (pr1 u' * pr1 v' + pr2 u' * pr2 v') (pr1 u' * pr2 v' + pr2 u' * pr1 v')) :=
|
||
calc
|
||
pr1 (pair (pr1 u * pr1 v + pr2 u * pr2 v) (pr1 u * pr2 v + pr2 u * pr1 v))
|
||
+ pr2 (pair (pr1 u' * pr1 v' + pr2 u' * pr2 v') (pr1 u' * pr2 v' + pr2 u' * pr1 v'))
|
||
= (pr1 u * pr1 v + pr2 u * pr2 v) + (pr1 u' * pr2 v' + pr2 u' * pr1 v') : by simp
|
||
... = (pr1 u * pr2 v + pr2 u * pr1 v) + (pr1 u' * pr1 v' + pr2 u' * pr2 v') : rel_mul_prep H1 H2
|
||
... = pr2 (pair (pr1 u * pr1 v + pr2 u * pr2 v) (pr1 u * pr2 v + pr2 u * pr1 v))
|
||
+ pr1 (pair (pr1 u' * pr1 v' + pr2 u' * pr2 v') (pr1 u' * pr2 v' + pr2 u' * pr1 v')) : by simp
|
||
|
||
definition mul : ℤ → ℤ → ℤ := quotient_map_binary quotient
|
||
(fun u v : ℕ × ℕ, pair (pr1 u * pr1 v + pr2 u * pr2 v) (pr1 u * pr2 v + pr2 u * pr1 v))
|
||
|
||
infixl `*` := int.mul
|
||
|
||
theorem mul_comp (n m k l : ℕ) :
|
||
psub (pair n m) * psub (pair k l) = psub (pair (n * k + m * l) (n * l + m * k)) :=
|
||
have H : ∀u v,
|
||
psub u * psub v = psub (pair (pr1 u * pr1 v + pr2 u * pr2 v) (pr1 u * pr2 v + pr2 u * pr1 v)),
|
||
from comp_quotient_map_binary_refl @rel_refl quotient @rel_mul,
|
||
trans (H (pair n m) (pair k l)) (by simp)
|
||
|
||
-- add_rewrite mul_comp
|
||
|
||
theorem mul_comm (a b : ℤ) : a * b = b * a :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
by simp
|
||
|
||
theorem mul_assoc (a b c : ℤ) : (a * b) * c = a * (b * c) :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
obtain (xc yc : ℕ) (Hc : c = psub (pair xc yc)), from destruct c,
|
||
by simp
|
||
|
||
theorem mul_left_comm : ∀a b c : ℤ, a * (b * c) = b * (a * c) :=
|
||
left_comm mul_comm mul_assoc
|
||
|
||
theorem mul_right_comm : ∀a b c : ℤ, a * b * c = a * c * b :=
|
||
right_comm mul_comm mul_assoc
|
||
|
||
-- ### interaction with other objects
|
||
|
||
theorem mul_zero_right (a : ℤ) : a * 0 = 0 :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
have H0 : 0 = psub (pair 0 0), from refl 0,
|
||
by simp
|
||
|
||
theorem mul_zero_left (a : ℤ) : 0 * a = 0 :=
|
||
subst (mul_comm a 0) (mul_zero_right a)
|
||
|
||
theorem mul_one_right (a : ℤ) : a * 1 = a :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
have H1 : 1 = psub (pair 1 0), from refl 1,
|
||
by simp
|
||
|
||
theorem mul_one_left (a : ℤ) : 1 * a = a :=
|
||
subst (mul_comm a 1) (mul_one_right a)
|
||
|
||
theorem mul_neg_right (a b : ℤ) : a * -b = -(a * b) :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
by simp
|
||
|
||
theorem mul_neg_left (a b : ℤ) : -a * b = -(a * b) :=
|
||
subst (mul_comm b a) (subst (mul_comm b (-a)) (mul_neg_right b a))
|
||
|
||
-- add_rewrite mul_neg_right mul_neg_left
|
||
|
||
theorem mul_neg_neg (a b : ℤ) : -a * -b = a * b :=
|
||
by simp
|
||
|
||
theorem mul_right_distr (a b c : ℤ) : (a + b) * c = a * c + b * c :=
|
||
obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
|
||
obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
|
||
obtain (xc yc : ℕ) (Hc : c = psub (pair xc yc)), from destruct c,
|
||
by simp
|
||
|
||
theorem mul_left_distr (a b c : ℤ) : a * (b + c) = a * b + a * c :=
|
||
calc
|
||
a * (b + c) = (b + c) * a : mul_comm a (b + c)
|
||
... = b * a + c * a : mul_right_distr b c a
|
||
... = a * b + c * a : {mul_comm b a}
|
||
... = a * b + a * c : {mul_comm c a}
|
||
|
||
theorem mul_sub_right_distr (a b c : ℤ) : (a - b) * c = a * c - b * c :=
|
||
calc
|
||
(a + -b) * c = a * c + -b * c : mul_right_distr a (-b) c
|
||
... = a * c + - (b * c) : {mul_neg_left b c}
|
||
|
||
theorem mul_sub_left_distr (a b c : ℤ) : a * (b - c) = a * b - a * c :=
|
||
calc
|
||
a * (b + -c) = a * b + a * -c : mul_left_distr a b (-c)
|
||
... = a * b + - (a * c) : {mul_neg_right a c}
|
||
|
||
theorem mul_of_nat (n m : ℕ) : of_nat n * of_nat m = n * m :=
|
||
have H : ∀n : ℕ, n = psub (pair n 0), from take n : ℕ, refl n,
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by simp
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theorem mul_to_nat (a b : ℤ) : (to_nat (a * b)) = #nat (to_nat a) * (to_nat b) :=
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obtain (xa ya : ℕ) (Ha : a = psub (pair xa ya)), from destruct a,
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obtain (xb yb : ℕ) (Hb : b = psub (pair xb yb)), from destruct b,
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have H : dist xa ya * dist xb yb = dist (xa * xb + ya * yb) (xa * yb + ya * xb),
|
||
from dist_mul_dist,
|
||
by simp
|
||
|
||
-- add_rewrite mul_zero_left mul_zero_right mul_one_right mul_one_left
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||
-- add_rewrite mul_comm mul_assoc mul_left_comm
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||
-- add_rewrite mul_distr_right mul_distr_left mul_of_nat mul_sub_distr_left mul_sub_distr_right
|
||
|
||
|
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-- ---------- inversion
|
||
|
||
theorem mul_eq_zero {a b : ℤ} (H : a * b = 0) : a = 0 ∨ b = 0 :=
|
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have H2 : (to_nat a) * (to_nat b) = 0, from
|
||
calc
|
||
(to_nat a) * (to_nat b) = (to_nat (a * b)) : symm (mul_to_nat a b)
|
||
... = (to_nat 0) : {H}
|
||
... = 0 : to_nat_of_nat 0,
|
||
have H3 : (to_nat a) = 0 ∨ (to_nat b) = 0, from mul_eq_zero H2,
|
||
or_imp_or H3
|
||
(assume H : (to_nat a) = 0, to_nat_eq_zero H)
|
||
(assume H : (to_nat b) = 0, to_nat_eq_zero H)
|
||
|
||
theorem mul_cancel_left_or {a b c : ℤ} (H : a * b = a * c) : a = 0 ∨ b = c :=
|
||
have H2 : a * (b - c) = 0, by simp,
|
||
have H3 : a = 0 ∨ b - c = 0, from mul_eq_zero H2,
|
||
or_imp_or_right H3 (assume H4 : b - c = 0, sub_eq_zero H4)
|
||
|
||
theorem mul_cancel_left {a b c : ℤ} (H1 : a ≠ 0) (H2 : a * b = a * c) : b = c :=
|
||
resolve_right (mul_cancel_left_or H2) H1
|
||
|
||
theorem mul_cancel_right_or {a b c : ℤ} (H : b * a = c * a) : a = 0 ∨ b = c :=
|
||
mul_cancel_left_or (subst (subst H (mul_comm b a)) (mul_comm c a))
|
||
|
||
theorem mul_cancel_right {a b c : ℤ} (H1 : c ≠ 0) (H2 : a * c = b * c) : a = b :=
|
||
resolve_right (mul_cancel_right_or H2) H1
|
||
|
||
theorem mul_ne_zero {a b : ℤ} (Ha : a ≠ 0) (Hb : b ≠ 0) : a * b ≠ 0 :=
|
||
not_intro
|
||
(assume H : a * b = 0,
|
||
or_elim (mul_eq_zero H)
|
||
(assume H2 : a = 0, absurd H2 Ha)
|
||
(assume H2 : b = 0, absurd H2 Hb))
|
||
|
||
theorem mul_ne_zero_left {a b : ℤ} (H : a * b ≠ 0) : a ≠ 0 :=
|
||
not_intro
|
||
(assume H2 : a = 0,
|
||
have H3 : a * b = 0, by simp,
|
||
absurd H3 H)
|
||
|
||
theorem mul_ne_zero_right {a b : ℤ} (H : a * b ≠ 0) : b ≠ 0 :=
|
||
mul_ne_zero_left (subst (mul_comm a b) H)
|
||
|
||
|
||
|
||
-- set_opaque rel true
|
||
-- set_opaque rep true
|
||
-- set_opaque of_nat true
|
||
-- set_opaque to_nat true
|
||
-- set_opaque neg true
|
||
-- set_opaque add true
|
||
-- set_opaque mul true
|
||
-- set_opaque le true
|
||
-- set_opaque lt true
|
||
-- set_opaque sign true
|
||
--transparent: sub ge gt
|
||
|
||
end int -- namespace int
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