250 lines
8.6 KiB
Text
250 lines
8.6 KiB
Text
/-
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Copyright (c) 2014 Microsoft Corporation. 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, Leonardo de Moura
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-/
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prelude
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import init.wf init.tactic init.num
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open eq.ops decidable or
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notation `ℕ` := nat
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namespace nat
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/- basic definitions on natural numbers -/
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inductive le (a : ℕ) : ℕ → Prop :=
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| refl : le a a
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| step : Π {b}, le a b → le a (succ b)
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definition nat_has_le [instance] [reducible] [priority nat.prio]: has_le nat := has_le.mk nat.le
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lemma le_refl [refl] : ∀ a : nat, a ≤ a :=
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le.refl
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protected definition lt [reducible] (n m : ℕ) := succ n ≤ m
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definition nat_has_lt [instance] [reducible] [priority nat.prio] : has_lt nat := has_lt.mk nat.lt
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definition pred [unfold 1] (a : nat) : nat :=
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nat.cases_on a zero (λ a₁, a₁)
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-- add is defined in init.num
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protected definition sub (a b : nat) : nat :=
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nat.rec_on b a (λ b₁, pred)
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protected definition mul (a b : nat) : nat :=
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nat.rec_on b zero (λ b₁ r, r + a)
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definition nat_has_sub [instance] [reducible] [priority nat.prio] : has_sub nat :=
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has_sub.mk nat.sub
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definition nat_has_mul [instance] [reducible] [priority nat.prio] : has_mul nat :=
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has_mul.mk nat.mul
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/- properties of ℕ -/
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protected definition is_inhabited [instance] : inhabited nat :=
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inhabited.mk zero
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protected definition has_decidable_eq [instance] [priority nat.prio] : ∀ x y : nat, decidable (x = y)
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| has_decidable_eq zero zero := inl rfl
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| has_decidable_eq (succ x) zero := inr (by contradiction)
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| has_decidable_eq zero (succ y) := inr (by contradiction)
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| has_decidable_eq (succ x) (succ y) :=
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match has_decidable_eq x y with
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| inl xeqy := inl (by rewrite xeqy)
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| inr xney := inr (λ h : succ x = succ y, by injection h with xeqy; exact absurd xeqy xney)
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end
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/- properties of inequality -/
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theorem le_of_eq {n m : ℕ} (p : n = m) : n ≤ m := p ▸ !le.refl
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theorem le_succ (n : ℕ) : n ≤ succ n := le.step !le.refl
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theorem pred_le (n : ℕ) : pred n ≤ n := by cases n;repeat constructor
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theorem le_succ_iff_true [simp] (n : ℕ) : n ≤ succ n ↔ true :=
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iff_true_intro (le_succ n)
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theorem pred_le_iff_true [simp] (n : ℕ) : pred n ≤ n ↔ true :=
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iff_true_intro (pred_le n)
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theorem le.trans {n m k : ℕ} (H1 : n ≤ m) : m ≤ k → n ≤ k :=
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le.rec H1 (λp H2, le.step)
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theorem le_succ_of_le {n m : ℕ} (H : n ≤ m) : n ≤ succ m := le.trans H !le_succ
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theorem le_of_succ_le {n m : ℕ} (H : succ n ≤ m) : n ≤ m := le.trans !le_succ H
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theorem le_of_lt {n m : ℕ} (H : n < m) : n ≤ m := le_of_succ_le H
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theorem succ_le_succ {n m : ℕ} : n ≤ m → succ n ≤ succ m :=
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le.rec !le.refl (λa b, le.step)
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theorem pred_le_pred {n m : ℕ} : n ≤ m → pred n ≤ pred m :=
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le.rec !le.refl (nat.rec (λa b, b) (λa b c, le.step))
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theorem le_of_succ_le_succ {n m : ℕ} : succ n ≤ succ m → n ≤ m :=
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pred_le_pred
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theorem le_succ_of_pred_le {n m : ℕ} : pred n ≤ m → n ≤ succ m :=
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nat.cases_on n le.step (λa, succ_le_succ)
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theorem not_succ_le_zero (n : ℕ) : ¬succ n ≤ 0 :=
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by intro H; cases H
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theorem succ_le_zero_iff_false (n : ℕ) : succ n ≤ 0 ↔ false :=
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iff_false_intro !not_succ_le_zero
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theorem not_succ_le_self : Π {n : ℕ}, ¬succ n ≤ n :=
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nat.rec !not_succ_le_zero (λa b c, b (le_of_succ_le_succ c))
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theorem succ_le_self_iff_false [simp] (n : ℕ) : succ n ≤ n ↔ false :=
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iff_false_intro not_succ_le_self
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theorem zero_le : ∀ (n : ℕ), 0 ≤ n :=
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nat.rec !le.refl (λa, le.step)
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theorem zero_le_iff_true [simp] (n : ℕ) : 0 ≤ n ↔ true :=
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iff_true_intro !zero_le
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theorem lt.step {n m : ℕ} : n < m → n < succ m := le.step
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theorem zero_lt_succ (n : ℕ) : 0 < succ n :=
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succ_le_succ !zero_le
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theorem zero_lt_succ_iff_true [simp] (n : ℕ) : 0 < succ n ↔ true :=
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iff_true_intro (zero_lt_succ n)
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theorem lt.trans {n m k : ℕ} (H1 : n < m) : m < k → n < k :=
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le.trans (le.step H1)
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theorem lt_of_le_of_lt {n m k : ℕ} (H1 : n ≤ m) : m < k → n < k :=
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le.trans (succ_le_succ H1)
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theorem lt_of_lt_of_le {n m k : ℕ} : n < m → m ≤ k → n < k := le.trans
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theorem lt.irrefl (n : ℕ) : ¬n < n := not_succ_le_self
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theorem lt_self_iff_false [simp] (n : ℕ) : n < n ↔ false :=
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iff_false_intro (lt.irrefl n)
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theorem self_lt_succ (n : ℕ) : n < succ n := !le.refl
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theorem self_lt_succ_iff_true [simp] (n : ℕ) : n < succ n ↔ true :=
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iff_true_intro (self_lt_succ n)
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theorem lt.base (n : ℕ) : n < succ n := !le.refl
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theorem le_lt_antisymm {n m : ℕ} (H1 : n ≤ m) (H2 : m < n) : false :=
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!lt.irrefl (lt_of_le_of_lt H1 H2)
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theorem le.antisymm {n m : ℕ} (H1 : n ≤ m) : m ≤ n → n = m :=
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le.cases_on H1 (λa, rfl) (λa b c, absurd (lt_of_le_of_lt b c) !lt.irrefl)
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theorem lt_le_antisymm {n m : ℕ} (H1 : n < m) (H2 : m ≤ n) : false :=
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le_lt_antisymm H2 H1
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theorem lt.asymm {n m : ℕ} (H1 : n < m) : ¬ m < n :=
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le_lt_antisymm (le_of_lt H1)
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theorem not_lt_zero (a : ℕ) : ¬ a < 0 := !not_succ_le_zero
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theorem lt_zero_iff_false [simp] (a : ℕ) : a < 0 ↔ false :=
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iff_false_intro (not_lt_zero a)
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theorem eq_or_lt_of_le {a b : ℕ} (H : a ≤ b) : a = b ∨ a < b :=
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le.cases_on H (inl rfl) (λn h, inr (succ_le_succ h))
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theorem le_of_eq_or_lt {a b : ℕ} (H : a = b ∨ a < b) : a ≤ b :=
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or.elim H !le_of_eq !le_of_lt
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-- less-than is well-founded
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definition lt.wf [instance] : well_founded lt :=
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well_founded.intro (nat.rec
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(!acc.intro (λn H, absurd H (not_lt_zero n)))
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(λn IH, !acc.intro (λm H,
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elim (eq_or_lt_of_le (le_of_succ_le_succ H))
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(λe, eq.substr e IH) (acc.inv IH))))
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definition measure {A : Type} : (A → ℕ) → A → A → Prop :=
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inv_image lt
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definition measure.wf {A : Type} (f : A → ℕ) : well_founded (measure f) :=
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inv_image.wf f lt.wf
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theorem succ_lt_succ {a b : ℕ} : a < b → succ a < succ b :=
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succ_le_succ
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theorem lt_of_succ_lt {a b : ℕ} : succ a < b → a < b :=
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le_of_succ_le
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theorem lt_of_succ_lt_succ {a b : ℕ} : succ a < succ b → a < b :=
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le_of_succ_le_succ
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definition decidable_le [instance] [priority nat.prio] : ∀ a b : nat, decidable (a ≤ b) :=
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nat.rec (λm, (decidable.inl !zero_le))
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(λn IH m, !nat.cases_on (decidable.inr (not_succ_le_zero n))
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(λm, decidable.rec (λH, inl (succ_le_succ H))
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(λH, inr (λa, H (le_of_succ_le_succ a))) (IH m)))
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definition decidable_lt [instance] [priority nat.prio] : ∀ a b : nat, decidable (a < b) :=
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λ a b, decidable_le (succ a) b
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theorem lt_or_ge (a b : ℕ) : a < b ∨ a ≥ b :=
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nat.rec (inr !zero_le) (λn, or.rec
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(λh, inl (le_succ_of_le h))
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(λh, elim (eq_or_lt_of_le h) (λe, inl (eq.subst e !le.refl)) inr)) b
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definition lt_ge_by_cases {a b : ℕ} {P : Type} (H1 : a < b → P) (H2 : a ≥ b → P) : P :=
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by_cases H1 (λh, H2 (elim !lt_or_ge (λa, absurd a h) (λa, a)))
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definition lt.by_cases {a b : ℕ} {P : Type} (H1 : a < b → P) (H2 : a = b → P) (H3 : b < a → P) : P :=
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lt_ge_by_cases H1 (λh₁,
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lt_ge_by_cases H3 (λh₂, H2 (le.antisymm h₂ h₁)))
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theorem lt.trichotomy (a b : ℕ) : a < b ∨ a = b ∨ b < a :=
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lt.by_cases (λH, inl H) (λH, inr (inl H)) (λH, inr (inr H))
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theorem eq_or_lt_of_not_lt {a b : ℕ} (hnlt : ¬ a < b) : a = b ∨ b < a :=
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or.rec_on (lt.trichotomy a b)
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(λ hlt, absurd hlt hnlt)
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(λ h, h)
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theorem lt_succ_of_le {a b : ℕ} : a ≤ b → a < succ b :=
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succ_le_succ
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theorem lt_of_succ_le {a b : ℕ} (h : succ a ≤ b) : a < b := h
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theorem succ_le_of_lt {a b : ℕ} (h : a < b) : succ a ≤ b := h
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theorem succ_sub_succ_eq_sub [simp] (a b : ℕ) : succ a - succ b = a - b :=
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nat.rec (by esimp) (λ b, congr_arg pred) b
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theorem sub_eq_succ_sub_succ (a b : ℕ) : a - b = succ a - succ b :=
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eq.symm !succ_sub_succ_eq_sub
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theorem zero_sub_eq_zero [simp] (a : ℕ) : 0 - a = 0 :=
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nat.rec rfl (λ a, congr_arg pred) a
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theorem zero_eq_zero_sub (a : ℕ) : 0 = 0 - a :=
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eq.symm !zero_sub_eq_zero
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theorem sub_le (a b : ℕ) : a - b ≤ a :=
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nat.rec_on b !le.refl (λ b₁, le.trans !pred_le)
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theorem sub_le_iff_true [simp] (a b : ℕ) : a - b ≤ a ↔ true :=
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iff_true_intro (sub_le a b)
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theorem sub_lt {a b : ℕ} (H1 : 0 < a) (H2 : 0 < b) : a - b < a :=
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!nat.cases_on (λh, absurd h !lt.irrefl)
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(λa h, succ_le_succ (!nat.cases_on (λh, absurd h !lt.irrefl)
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(λb c, eq.substr !succ_sub_succ_eq_sub !sub_le) H2)) H1
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theorem sub_lt_succ (a b : ℕ) : a - b < succ a :=
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lt_succ_of_le !sub_le
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theorem sub_lt_succ_iff_true [simp] (a b : ℕ) : a - b < succ a ↔ true :=
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iff_true_intro !sub_lt_succ
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end nat
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