From 1dba5d4d5325ac0a9a05255fa6de4f5c34e19244 Mon Sep 17 00:00:00 2001
From: ammkrn <ammkrn@tuta.io>
Date: Tue, 5 Oct 2021 12:20:26 +0000
Subject: [PATCH] feat: List.product (#59)

---
 Mathlib/Data/List/Basic.lean | 11 +++++++++++
 Mathlib/Logic/Basic.lean     | 28 ++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/Mathlib/Data/List/Basic.lean b/Mathlib/Data/List/Basic.lean
index c6376cbb7a15..d1257dad0af1 100644
--- a/Mathlib/Data/List/Basic.lean
+++ b/Mathlib/Data/List/Basic.lean
@@ -1117,4 +1117,15 @@ filter (fun a => a ∈ l₂) l₁
   | nil => simp [List.inter, mem_filter]
   | cons a l' ih => simp [List.inter, mem_filter, decide_eq_true_iff (x ∈ l₂)]
 
+def product (l1 : List α) (l2 : List β) : List (α × β) :=
+l1.bind (fun a => l2.map (Prod.mk a))
+
+/--
+List.prod satisfies a specification of cartesian product on lists.
+-/
+theorem product_spec (xs : List α) (ys : List β) (x : α) (y : β) : (x, y) ∈ product xs ys <-> (x ∈ xs ∧ y ∈ ys) := by
+apply Iff.intro
+case mp => simp only [List.product, and_imp, exists_prop, List.mem_map, Prod.mk.injEq, exists_eq_right_right', List.mem_bind]; exact And.intro
+case mpr => simp only [product, mem_bind, mem_map, Prod.mk.injEq, exists_eq_right_right', exists_prop]; exact id
+
 end List
diff --git a/Mathlib/Logic/Basic.lean b/Mathlib/Logic/Basic.lean
index 547a02980542..e57da06bb354 100644
--- a/Mathlib/Logic/Basic.lean
+++ b/Mathlib/Logic/Basic.lean
@@ -231,6 +231,17 @@ theorem xor_comm (a b) : xor a b = xor b a := by simp [xor, and_comm, or_comm]
 
 /-! ### Declarations about `and` -/
 
+theorem and_symm_right (a b : α) (p : Prop) : p ∧ a = b <-> p ∧ b = a :=
+Iff.intro
+  (fun ⟨hp, a_eq_b⟩ => ⟨hp, a_eq_b.symm⟩)
+  (fun ⟨hp, b_eq_a⟩ => ⟨hp, b_eq_a.symm⟩)
+
+theorem and_symm_left (a b : α) (p : Prop) : a = b ∧ p <-> b = a ∧ p :=
+Iff.intro
+  (fun ⟨a_eq_b, hp⟩ => ⟨a_eq_b.symm, hp⟩)
+  (fun ⟨b_eq_a, hp⟩ => ⟨b_eq_a.symm, hp⟩)
+
+
 theorem and_congr_left (h : c → (a ↔ b)) : a ∧ c ↔ b ∧ c :=
 And.comm.trans $ (and_congr_right h).trans And.comm
 
@@ -689,6 +700,23 @@ by simp [And.comm]
 @[simp] theorem exists_eq_left' {p : α → Prop} {a' : α} : (∃ a, a' = a ∧ p a) ↔ p a' :=
 by simp [@eq_comm _ a']
 
+@[simp] theorem exists_eq_right_right {α : Sort _} {p : α → Prop} {b : Prop} {a' : α} :
+(∃ (a : α), p a ∧ b ∧ a = a') ↔ p a' ∧ b :=
+  Iff.intro
+  (fun ⟨_, ⟨p_a, hb, a_eq_a'⟩⟩ => And.intro (a_eq_a' ▸ p_a) hb)
+  (fun ⟨p_a', hb⟩ => Exists.intro a' ⟨p_a', hb, (rfl : a' = a')⟩)
+
+@[simp] theorem exists_eq_right_right' {α : Sort _} {p : α → Prop} {b : Prop} {a' : α} :
+(∃ (a : α), p a ∧ b ∧ a' = a) ↔ p a' ∧ b :=
+  Iff.intro
+  (fun ⟨_, ⟨p_a, hb, a_eq_a'⟩⟩ => And.intro (a_eq_a' ▸ p_a) hb)
+  (fun ⟨p_a', hb⟩ => Exists.intro a' ⟨p_a', hb, (rfl : a' = a')⟩)
+
+
+@[simp]
+theorem exists_prop {p q : Prop} : (∃ h : p, q) ↔ p ∧ q :=
+Iff.intro (fun ⟨hp, hq⟩ => And.intro hp hq) (fun ⟨hp, hq⟩ => Exists.intro hp hq)
+
 @[simp] theorem exists_apply_eq_apply {α β : Type _} (f : α → β) (a' : α) : ∃ a, f a = f a' :=
 ⟨a', rfl⟩