513 lines
17 KiB
Text
513 lines
17 KiB
Text
--- Copyright (c) 2014 Floris van Doorn. All rights reserved.
|
||
--- Released under Apache 2.0 license as described in the file LICENSE.
|
||
--- Author: Floris van Doorn
|
||
|
||
-- data.nat.sub
|
||
-- ============
|
||
--
|
||
-- Subtraction on the natural numbers, as well as min, max, and distance.
|
||
|
||
import data.nat.order
|
||
import tools.fake_simplifier
|
||
|
||
using nat eq_ops tactic
|
||
using helper_tactics
|
||
using fake_simplifier
|
||
|
||
namespace nat
|
||
|
||
|
||
-- subtraction
|
||
-- -----------
|
||
|
||
definition sub (n m : ℕ) : nat := nat_rec n (fun m x, pred x) m
|
||
infixl `-` := sub
|
||
|
||
theorem sub_zero_right (n : ℕ) : n - 0 = n
|
||
|
||
theorem sub_succ_right (n m : ℕ) : n - succ m = pred (n - m)
|
||
|
||
opaque_hint (hiding sub)
|
||
|
||
theorem sub_zero_left (n : ℕ) : 0 - n = 0 :=
|
||
induction_on n (sub_zero_right 0)
|
||
(take k : nat,
|
||
assume IH : 0 - k = 0,
|
||
calc
|
||
0 - succ k = pred (0 - k) : sub_succ_right 0 k
|
||
... = pred 0 : {IH}
|
||
... = 0 : pred_zero)
|
||
--(
|
||
--theorem sub_succ_left (n m : ℕ) : pred (succ n - m) = n - m
|
||
-- :=
|
||
-- induction_on m
|
||
-- (calc
|
||
-- pred (succ n - 0) = pred (succ n) : {sub_zero_right (succ n)}
|
||
-- ... = n : pred_succ n
|
||
-- ... = n - 0 : symm (sub_zero_right n))
|
||
-- (take k : nat,
|
||
-- assume IH : pred (succ n - k) = n - k,
|
||
-- _)
|
||
--)
|
||
|
||
--succ_sub_succ
|
||
theorem sub_succ_succ (n m : ℕ) : succ n - succ m = n - m :=
|
||
induction_on m
|
||
(calc
|
||
succ n - 1 = pred (succ n - 0) : sub_succ_right (succ n) 0
|
||
... = pred (succ n) : {sub_zero_right (succ n)}
|
||
... = n : pred_succ n
|
||
... = n - 0 : symm (sub_zero_right n))
|
||
(take k : nat,
|
||
assume IH : succ n - succ k = n - k,
|
||
calc
|
||
succ n - succ (succ k) = pred (succ n - succ k) : sub_succ_right (succ n) (succ k)
|
||
... = pred (n - k) : {IH}
|
||
... = n - succ k : symm (sub_succ_right n k))
|
||
|
||
theorem sub_self (n : ℕ) : n - n = 0 :=
|
||
induction_on n (sub_zero_right 0) (take k IH, trans (sub_succ_succ k k) IH)
|
||
|
||
-- TODO: add_sub_add_right
|
||
theorem sub_add_add_right (n k m : ℕ) : (n + k) - (m + k) = n - m :=
|
||
induction_on k
|
||
(calc
|
||
(n + 0) - (m + 0) = n - (m + 0) : {add_zero_right _}
|
||
... = n - m : {add_zero_right _})
|
||
(take l : nat,
|
||
assume IH : (n + l) - (m + l) = n - m,
|
||
calc
|
||
(n + succ l) - (m + succ l) = succ (n + l) - (m + succ l) : {add_succ_right _ _}
|
||
... = succ (n + l) - succ (m + l) : {add_succ_right _ _}
|
||
... = (n + l) - (m + l) : sub_succ_succ _ _
|
||
... = n - m : IH)
|
||
|
||
theorem sub_add_add_left (k n m : ℕ) : (k + n) - (k + m) = n - m :=
|
||
add_comm m k ▸ add_comm n k ▸ sub_add_add_right n k m
|
||
|
||
-- TODO: add_sub_inv
|
||
theorem sub_add_left (n m : ℕ) : n + m - m = n :=
|
||
induction_on m
|
||
((add_zero_right n)⁻¹ ▸ sub_zero_right n)
|
||
(take k : ℕ,
|
||
assume IH : n + k - k = n,
|
||
calc
|
||
n + succ k - succ k = succ (n + k) - succ k : {add_succ_right n k}
|
||
... = n + k - k : sub_succ_succ _ _
|
||
... = n : IH)
|
||
|
||
-- TODO: add_sub_inv'
|
||
theorem sub_add_left2 (n m : ℕ) : n + m - n = m :=
|
||
add_comm m n ▸ sub_add_left m n
|
||
|
||
theorem sub_sub (n m k : ℕ) : n - m - k = n - (m + k) :=
|
||
induction_on k
|
||
(calc
|
||
n - m - 0 = n - m : sub_zero_right _
|
||
... = n - (m + 0) : {symm (add_zero_right m)})
|
||
(take l : nat,
|
||
assume IH : n - m - l = n - (m + l),
|
||
calc
|
||
n - m - succ l = pred (n - m - l) : sub_succ_right (n - m) l
|
||
... = pred (n - (m + l)) : {IH}
|
||
... = n - succ (m + l) : symm (sub_succ_right n (m + l))
|
||
... = n - (m + succ l) : {symm (add_succ_right m l)})
|
||
|
||
theorem succ_sub_sub (n m k : ℕ) : succ n - m - succ k = n - m - k :=
|
||
calc
|
||
succ n - m - succ k = succ n - (m + succ k) : sub_sub _ _ _
|
||
... = succ n - succ (m + k) : {add_succ_right m k}
|
||
... = n - (m + k) : sub_succ_succ _ _
|
||
... = n - m - k : symm (sub_sub n m k)
|
||
|
||
theorem sub_add_right_eq_zero (n m : ℕ) : n - (n + m) = 0 :=
|
||
calc
|
||
n - (n + m) = n - n - m : symm (sub_sub n n m)
|
||
... = 0 - m : {sub_self n}
|
||
... = 0 : sub_zero_left m
|
||
|
||
theorem sub_comm (m n k : ℕ) : m - n - k = m - k - n :=
|
||
calc
|
||
m - n - k = m - (n + k) : sub_sub m n k
|
||
... = m - (k + n) : {add_comm n k}
|
||
... = m - k - n : symm (sub_sub m k n)
|
||
|
||
theorem sub_one (n : ℕ) : n - 1 = pred n :=
|
||
calc
|
||
n - 1 = pred (n - 0) : sub_succ_right n 0
|
||
... = pred n : {sub_zero_right n}
|
||
|
||
theorem succ_sub_one (n : ℕ) : succ n - 1 = n :=
|
||
trans (sub_succ_succ n 0) (sub_zero_right n)
|
||
|
||
-- add_rewrite sub_add_left
|
||
|
||
-- ### interaction with multiplication
|
||
|
||
theorem mul_pred_left (n m : ℕ) : pred n * m = n * m - m :=
|
||
induction_on n
|
||
(calc
|
||
pred 0 * m = 0 * m : {pred_zero}
|
||
... = 0 : mul_zero_left _
|
||
... = 0 - m : symm (sub_zero_left m)
|
||
... = 0 * m - m : {symm (mul_zero_left m)})
|
||
(take k : nat,
|
||
assume IH : pred k * m = k * m - m,
|
||
calc
|
||
pred (succ k) * m = k * m : {pred_succ k}
|
||
... = k * m + m - m : symm (sub_add_left _ _)
|
||
... = succ k * m - m : {symm (mul_succ_left k m)})
|
||
|
||
theorem mul_pred_right (n m : ℕ) : n * pred m = n * m - n :=
|
||
calc n * pred m = pred m * n : mul_comm _ _
|
||
... = m * n - n : mul_pred_left m n
|
||
... = n * m - n : {mul_comm m n}
|
||
|
||
theorem mul_sub_distr_right (n m k : ℕ) : (n - m) * k = n * k - m * k :=
|
||
induction_on m
|
||
(calc
|
||
(n - 0) * k = n * k : {sub_zero_right n}
|
||
... = n * k - 0 : symm (sub_zero_right _)
|
||
... = n * k - 0 * k : {symm (mul_zero_left _)})
|
||
(take l : nat,
|
||
assume IH : (n - l) * k = n * k - l * k,
|
||
calc
|
||
(n - succ l) * k = pred (n - l) * k : {sub_succ_right n l}
|
||
... = (n - l) * k - k : mul_pred_left _ _
|
||
... = n * k - l * k - k : {IH}
|
||
... = n * k - (l * k + k) : sub_sub _ _ _
|
||
... = n * k - (succ l * k) : {symm (mul_succ_left l k)})
|
||
|
||
theorem mul_sub_distr_left (n m k : ℕ) : n * (m - k) = n * m - n * k :=
|
||
calc
|
||
n * (m - k) = (m - k) * n : mul_comm _ _
|
||
... = m * n - k * n : mul_sub_distr_right _ _ _
|
||
... = n * m - k * n : {mul_comm _ _}
|
||
... = n * m - n * k : {mul_comm _ _}
|
||
|
||
-- ### interaction with inequalities
|
||
|
||
theorem succ_sub {m n : ℕ} : m ≥ n → succ m - n = succ (m - n) :=
|
||
sub_induction n m
|
||
(take k,
|
||
assume H : 0 ≤ k,
|
||
calc
|
||
succ k - 0 = succ k : sub_zero_right (succ k)
|
||
... = succ (k - 0) : {symm (sub_zero_right k)})
|
||
(take k,
|
||
assume H : succ k ≤ 0,
|
||
absurd H (not_succ_zero_le k))
|
||
(take k l,
|
||
assume IH : k ≤ l → succ l - k = succ (l - k),
|
||
take H : succ k ≤ succ l,
|
||
calc
|
||
succ (succ l) - succ k = succ l - k : sub_succ_succ (succ l) k
|
||
... = succ (l - k) : IH (succ_le_cancel H)
|
||
... = succ (succ l - succ k) : {symm (sub_succ_succ l k)})
|
||
|
||
theorem le_imp_sub_eq_zero {n m : ℕ} (H : n ≤ m) : n - m = 0 :=
|
||
obtain (k : ℕ) (Hk : n + k = m), from le_elim H, Hk ▸ sub_add_right_eq_zero n k
|
||
|
||
theorem add_sub_le {n m : ℕ} : n ≤ m → n + (m - n) = m :=
|
||
sub_induction n m
|
||
(take k,
|
||
assume H : 0 ≤ k,
|
||
calc
|
||
0 + (k - 0) = k - 0 : add_zero_left (k - 0)
|
||
... = k : sub_zero_right k)
|
||
(take k, assume H : succ k ≤ 0, absurd H (not_succ_zero_le k))
|
||
(take k l,
|
||
assume IH : k ≤ l → k + (l - k) = l,
|
||
take H : succ k ≤ succ l,
|
||
calc
|
||
succ k + (succ l - succ k) = succ k + (l - k) : {sub_succ_succ l k}
|
||
... = succ (k + (l - k)) : add_succ_left k (l - k)
|
||
... = succ l : {IH (succ_le_cancel H)})
|
||
|
||
theorem add_sub_ge_left {n m : ℕ} : n ≥ m → n - m + m = n :=
|
||
add_comm m (n - m) ▸ add_sub_le
|
||
|
||
theorem add_sub_ge {n m : ℕ} (H : n ≥ m) : n + (m - n) = n :=
|
||
calc
|
||
n + (m - n) = n + 0 : {le_imp_sub_eq_zero H}
|
||
... = n : add_zero_right n
|
||
|
||
theorem add_sub_le_left {n m : ℕ} : n ≤ m → n - m + m = m :=
|
||
add_comm m (n - m) ▸ add_sub_ge
|
||
|
||
theorem le_add_sub_left (n m : ℕ) : n ≤ n + (m - n) :=
|
||
or_elim (le_total n m)
|
||
(assume H : n ≤ m, (add_sub_le H)⁻¹ ▸ H)
|
||
(assume H : m ≤ n, (add_sub_ge H)⁻¹ ▸ le_refl n)
|
||
|
||
theorem le_add_sub_right (n m : ℕ) : m ≤ n + (m - n) :=
|
||
or_elim (le_total n m)
|
||
(assume H : n ≤ m, subst (symm (add_sub_le H)) (le_refl m))
|
||
(assume H : m ≤ n, subst (symm (add_sub_ge H)) H)
|
||
|
||
theorem sub_split {P : ℕ → Prop} {n m : ℕ} (H1 : n ≤ m → P 0) (H2 : ∀k, m + k = n -> P k)
|
||
: P (n - m) :=
|
||
or_elim (le_total n m)
|
||
(assume H3 : n ≤ m, subst (symm (le_imp_sub_eq_zero H3)) (H1 H3))
|
||
(assume H3 : m ≤ n, H2 (n - m) (add_sub_le H3))
|
||
|
||
theorem sub_le_self (n m : ℕ) : n - m ≤ n :=
|
||
sub_split
|
||
(assume H : n ≤ m, zero_le n)
|
||
(take k : ℕ, assume H : m + k = n, le_intro (subst (add_comm m k) H))
|
||
|
||
theorem le_elim_sub (n m : ℕ) (H : n ≤ m) : ∃k, m - k = n :=
|
||
obtain (k : ℕ) (Hk : n + k = m), from le_elim H,
|
||
exists_intro k
|
||
(calc
|
||
m - k = n + k - k : {symm Hk}
|
||
... = n : sub_add_left n k)
|
||
|
||
theorem add_sub_assoc {m k : ℕ} (H : k ≤ m) (n : ℕ) : n + m - k = n + (m - k) :=
|
||
have l1 : k ≤ m → n + m - k = n + (m - k), from
|
||
sub_induction k m
|
||
(take m : ℕ,
|
||
assume H : 0 ≤ m,
|
||
calc
|
||
n + m - 0 = n + m : sub_zero_right (n + m)
|
||
... = n + (m - 0) : {symm (sub_zero_right m)})
|
||
(take k : ℕ, assume H : succ k ≤ 0, absurd H (not_succ_zero_le k))
|
||
(take k m,
|
||
assume IH : k ≤ m → n + m - k = n + (m - k),
|
||
take H : succ k ≤ succ m,
|
||
calc
|
||
n + succ m - succ k = succ (n + m) - succ k : {add_succ_right n m}
|
||
... = n + m - k : sub_succ_succ (n + m) k
|
||
... = n + (m - k) : IH (succ_le_cancel H)
|
||
... = n + (succ m - succ k) : {symm (sub_succ_succ m k)}),
|
||
l1 H
|
||
|
||
theorem sub_eq_zero_imp_le {n m : ℕ} : n - m = 0 → n ≤ m :=
|
||
sub_split
|
||
(assume H1 : n ≤ m, assume H2 : 0 = 0, H1)
|
||
(take k : ℕ,
|
||
assume H1 : m + k = n,
|
||
assume H2 : k = 0,
|
||
have H3 : n = m, from subst (add_zero_right m) (subst H2 (symm H1)),
|
||
subst H3 (le_refl n))
|
||
|
||
theorem sub_sub_split {P : ℕ → ℕ → Prop} {n m : ℕ} (H1 : ∀k, n = m + k -> P k 0)
|
||
(H2 : ∀k, m = n + k → P 0 k) : P (n - m) (m - n) :=
|
||
or_elim (le_total n m)
|
||
(assume H3 : n ≤ m,
|
||
le_imp_sub_eq_zero H3⁻¹ ▸ (H2 (m - n) (add_sub_le H3⁻¹)))
|
||
(assume H3 : m ≤ n,
|
||
le_imp_sub_eq_zero H3⁻¹ ▸ (H1 (n - m) (add_sub_le H3⁻¹)))
|
||
|
||
theorem sub_intro {n m k : ℕ} (H : n + m = k) : k - n = m :=
|
||
have H2 : k - n + n = m + n, from
|
||
calc
|
||
k - n + n = k : add_sub_ge_left (le_intro H)
|
||
... = n + m : symm H
|
||
... = m + n : add_comm n m,
|
||
add_cancel_right H2
|
||
|
||
theorem sub_lt {x y : ℕ} (xpos : x > 0) (ypos : y > 0) : x - y < x :=
|
||
obtain (x' : ℕ) (xeq : x = succ x'), from pos_imp_eq_succ xpos,
|
||
obtain (y' : ℕ) (yeq : y = succ y'), from pos_imp_eq_succ ypos,
|
||
have xsuby_eq : x - y = x' - y', from
|
||
calc
|
||
x - y = succ x' - y : {xeq}
|
||
... = succ x' - succ y' : {yeq}
|
||
... = x' - y' : sub_succ_succ _ _,
|
||
have H1 : x' - y' ≤ x', from sub_le_self _ _,
|
||
have H2 : x' < succ x', from self_lt_succ _,
|
||
show x - y < x, from xeq⁻¹ ▸ xsuby_eq⁻¹ ▸ le_lt_trans H1 H2
|
||
|
||
theorem sub_le_right {n m : ℕ} (H : n ≤ m) (k : nat) : n - k ≤ m - k :=
|
||
obtain (l : ℕ) (Hl : n + l = m), from le_elim H,
|
||
or_elim (le_total n k)
|
||
(assume H2 : n ≤ k, (le_imp_sub_eq_zero H2)⁻¹ ▸ zero_le (m - k))
|
||
(assume H2 : k ≤ n,
|
||
have H3 : n - k + l = m - k, from
|
||
calc
|
||
n - k + l = l + (n - k) : by simp
|
||
... = l + n - k : symm (add_sub_assoc H2 l)
|
||
... = n + l - k : {add_comm l n}
|
||
... = m - k : {Hl},
|
||
le_intro H3)
|
||
|
||
theorem sub_le_left {n m : ℕ} (H : n ≤ m) (k : nat) : k - m ≤ k - n :=
|
||
obtain (l : ℕ) (Hl : n + l = m), from le_elim H,
|
||
sub_split
|
||
(assume H2 : k ≤ m, zero_le (k - n))
|
||
(take m' : ℕ,
|
||
assume Hm : m + m' = k,
|
||
have H3 : n ≤ k, from le_trans H (le_intro Hm),
|
||
have H4 : m' + l + n = k - n + n, from
|
||
calc
|
||
m' + l + n = n + l + m' : by simp
|
||
... = m + m' : {Hl}
|
||
... = k : Hm
|
||
... = k - n + n : symm (add_sub_ge_left H3),
|
||
le_intro (add_cancel_right H4))
|
||
|
||
-- theorem sub_lt_cancel_right {n m k : ℕ) (H : n - k < m - k) : n < m
|
||
-- :=
|
||
-- _
|
||
|
||
-- theorem sub_lt_cancel_left {n m k : ℕ) (H : n - m < n - k) : k < m
|
||
-- :=
|
||
-- _
|
||
|
||
theorem sub_triangle_inequality (n m k : ℕ) : n - k ≤ (n - m) + (m - k) :=
|
||
sub_split
|
||
(assume H : n ≤ m, (add_zero_left (m - k))⁻¹ ▸ sub_le_right H k)
|
||
(take mn : ℕ,
|
||
assume Hmn : m + mn = n,
|
||
sub_split
|
||
(assume H : m ≤ k,
|
||
have H2 : n - k ≤ n - m, from sub_le_left H n,
|
||
have H3 : n - k ≤ mn, from sub_intro Hmn ▸ H2,
|
||
show n - k ≤ mn + 0, from (add_zero_right mn)⁻¹ ▸ H3)
|
||
(take km : ℕ,
|
||
assume Hkm : k + km = m,
|
||
have H : k + (mn + km) = n, from
|
||
calc
|
||
k + (mn + km) = k + km + mn : by simp
|
||
... = m + mn : {Hkm}
|
||
... = n : Hmn,
|
||
have H2 : n - k = mn + km, from sub_intro H,
|
||
H2 ▸ (le_refl (n - k))))
|
||
|
||
|
||
-- add_rewrite sub_self mul_sub_distr_left mul_sub_distr_right
|
||
|
||
|
||
-- Max, min, iteration, and absolute difference
|
||
-- --------------------------------------------
|
||
|
||
definition max (n m : ℕ) : ℕ := n + (m - n)
|
||
definition min (n m : ℕ) : ℕ := m - (m - n)
|
||
|
||
theorem max_le {n m : ℕ} (H : n ≤ m) : n + (m - n) = m := add_sub_le H
|
||
|
||
theorem max_ge {n m : ℕ} (H : n ≥ m) : n + (m - n) = n := add_sub_ge H
|
||
|
||
theorem left_le_max (n m : ℕ) : n ≤ n + (m - n) := le_add_sub_left n m
|
||
|
||
theorem right_le_max (n m : ℕ) : m ≤ max n m := le_add_sub_right n m
|
||
|
||
-- ### absolute difference
|
||
|
||
-- This section is still incomplete
|
||
|
||
definition dist (n m : ℕ) := (n - m) + (m - n)
|
||
|
||
theorem dist_comm (n m : ℕ) : dist n m = dist m n :=
|
||
add_comm (n - m) (m - n)
|
||
|
||
theorem dist_self (n : ℕ) : dist n n = 0 :=
|
||
calc
|
||
(n - n) + (n - n) = 0 + 0 : by simp
|
||
... = 0 : by simp
|
||
|
||
theorem dist_eq_zero {n m : ℕ} (H : dist n m = 0) : n = m :=
|
||
have H2 : n - m = 0, from add_eq_zero_left H,
|
||
have H3 : n ≤ m, from sub_eq_zero_imp_le H2,
|
||
have H4 : m - n = 0, from add_eq_zero_right H,
|
||
have H5 : m ≤ n, from sub_eq_zero_imp_le H4,
|
||
le_antisym H3 H5
|
||
|
||
theorem dist_le {n m : ℕ} (H : n ≤ m) : dist n m = m - n :=
|
||
calc
|
||
dist n m = 0 + (m - n) : {le_imp_sub_eq_zero H}
|
||
... = m - n : add_zero_left (m - n)
|
||
|
||
theorem dist_ge {n m : ℕ} (H : n ≥ m) : dist n m = n - m :=
|
||
dist_comm m n ▸ dist_le H
|
||
|
||
theorem dist_zero_right (n : ℕ) : dist n 0 = n :=
|
||
trans (dist_ge (zero_le n)) (sub_zero_right n)
|
||
|
||
theorem dist_zero_left (n : ℕ) : dist 0 n = n :=
|
||
trans (dist_le (zero_le n)) (sub_zero_right n)
|
||
|
||
theorem dist_intro {n m k : ℕ} (H : n + m = k) : dist k n = m :=
|
||
calc
|
||
dist k n = k - n : dist_ge (le_intro H)
|
||
... = m : sub_intro H
|
||
|
||
theorem dist_add_right (n k m : ℕ) : dist (n + k) (m + k) = dist n m :=
|
||
calc
|
||
dist (n + k) (m + k) = ((n+k) - (m+k)) + ((m+k)-(n+k)) : refl _
|
||
... = (n - m) + ((m + k) - (n + k)) : {sub_add_add_right _ _ _}
|
||
... = (n - m) + (m - n) : {sub_add_add_right _ _ _}
|
||
|
||
theorem dist_add_left (k n m : ℕ) : dist (k + n) (k + m) = dist n m :=
|
||
add_comm m k ▸ add_comm n k ▸ dist_add_right n k m
|
||
|
||
-- add_rewrite dist_self dist_add_right dist_add_left dist_zero_left dist_zero_right
|
||
|
||
theorem dist_ge_add_right {n m : ℕ} (H : n ≥ m) : dist n m + m = n :=
|
||
calc
|
||
dist n m + m = n - m + m : {dist_ge H}
|
||
... = n : add_sub_ge_left H
|
||
|
||
theorem dist_eq_intro {n m k l : ℕ} (H : n + m = k + l) : dist n k = dist l m :=
|
||
calc
|
||
dist n k = dist (n + m) (k + m) : symm (dist_add_right n m k)
|
||
... = dist (k + l) (k + m) : {H}
|
||
... = dist l m : dist_add_left k l m
|
||
|
||
theorem dist_sub_move_add {n m : ℕ} (H : n ≥ m) (k : ℕ) : dist (n - m) k = dist n (k + m) :=
|
||
have H2 : n - m + (k + m) = k + n, from
|
||
calc
|
||
n - m + (k + m) = n - m + m + k : by simp
|
||
... = n + k : {add_sub_ge_left H}
|
||
... = k + n : by simp,
|
||
dist_eq_intro H2
|
||
|
||
theorem dist_sub_move_add' {k m : ℕ} (H : k ≥ m) (n : ℕ) : dist n (k - m) = dist (n + m) k :=
|
||
subst (subst (dist_sub_move_add H n) (dist_comm (k - m) n)) (dist_comm k (n + m))
|
||
|
||
--triangle inequality formulated with dist
|
||
theorem triangle_inequality (n m k : ℕ) : dist n k ≤ dist n m + dist m k :=
|
||
have H : (n - m) + (m - k) + ((k - m) + (m - n)) = (n - m) + (m - n) + ((m - k) + (k - m)),
|
||
by simp,
|
||
H ▸ add_le (sub_triangle_inequality n m k) (sub_triangle_inequality k m n)
|
||
|
||
theorem dist_add_le_add_dist (n m k l : ℕ) : dist (n + m) (k + l) ≤ dist n k + dist m l :=
|
||
have H : dist (n + m) (k + m) + dist (k + m) (k + l) = dist n k + dist m l, from
|
||
calc
|
||
_ = dist n k + dist (k + m) (k + l) : {dist_add_right n m k}
|
||
... = _ : {dist_add_left k m l},
|
||
H ▸ (triangle_inequality (n + m) (k + m) (k + l))
|
||
|
||
--interaction with multiplication
|
||
|
||
theorem dist_mul_left (k n m : ℕ) : dist (k * n) (k * m) = k * dist n m :=
|
||
have H : ∀n m, dist n m = n - m + (m - n), from take n m, refl _,
|
||
by simp
|
||
|
||
theorem dist_mul_right (n k m : ℕ) : dist (n * k) (m * k) = dist n m * k :=
|
||
have H : ∀n m, dist n m = n - m + (m - n), from take n m, refl _,
|
||
by simp
|
||
|
||
-- add_rewrite dist_mul_right dist_mul_left dist_comm
|
||
|
||
--needed to prove of_nat a * of_nat b = of_nat (a * b) in int
|
||
theorem dist_mul_dist (n m k l : ℕ) : dist n m * dist k l = dist (n * k + m * l) (n * l + m * k) :=
|
||
have aux : ∀k l, k ≥ l → dist n m * dist k l = dist (n * k + m * l) (n * l + m * k), from
|
||
take k l : ℕ,
|
||
assume H : k ≥ l,
|
||
have H2 : m * k ≥ m * l, from mul_le_left H m,
|
||
have H3 : n * l + m * k ≥ m * l, from le_trans H2 (le_add_left _ _),
|
||
calc
|
||
dist n m * dist k l = dist n m * (k - l) : {dist_ge H}
|
||
... = dist (n * (k - l)) (m * (k - l)) : symm (dist_mul_right n (k - l) m)
|
||
... = dist (n * k - n * l) (m * k - m * l) : by simp
|
||
... = dist (n * k) (m * k - m * l + n * l) : dist_sub_move_add (mul_le_left H n) _
|
||
... = dist (n * k) (n * l + (m * k - m * l)) : {add_comm _ _}
|
||
... = dist (n * k) (n * l + m * k - m * l) : {symm (add_sub_assoc H2 (n * l))}
|
||
... = dist (n * k + m * l) (n * l + m * k) : dist_sub_move_add' H3 _,
|
||
or_elim (le_total k l)
|
||
(assume H : k ≤ l, dist_comm l k ▸ dist_comm _ _ ▸ aux l k H)
|
||
(assume H : l ≤ k, aux k l H)
|
||
|
||
end nat
|