215 lines
7.7 KiB
Text
215 lines
7.7 KiB
Text
/-
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Copyright (c) 2016 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: Jeremy Avigad, Leonardo de Moura
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-/
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prelude
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import init.algebra.group
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/- Make sure instances defined in this file have lower priority than the ones
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defined for concrete structures -/
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set_option default_priority 100
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universe u
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class distrib (α : Type u) extends has_mul α, has_add α :=
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(left_distrib : ∀ a b c : α, a * (b + c) = (a * b) + (a * c))
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(right_distrib : ∀ a b c : α, (a + b) * c = (a * c) + (b * c))
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variable {α : Type u}
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lemma left_distrib [distrib α] (a b c : α) : a * (b + c) = a * b + a * c :=
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distrib.left_distrib a b c
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def mul_add := @left_distrib
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lemma right_distrib [distrib α] (a b c : α) : (a + b) * c = a * c + b * c :=
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distrib.right_distrib a b c
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def add_mul := @right_distrib
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class mul_zero_class (α : Type u) extends has_mul α, has_zero α :=
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(zero_mul : ∀ a : α, 0 * a = 0)
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(mul_zero : ∀ a : α, a * 0 = 0)
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@[simp] lemma zero_mul [mul_zero_class α] (a : α) : 0 * a = 0 :=
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mul_zero_class.zero_mul a
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@[simp] lemma mul_zero [mul_zero_class α] (a : α) : a * 0 = 0 :=
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mul_zero_class.mul_zero a
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class zero_ne_one_class (α : Type u) extends has_zero α, has_one α :=
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(zero_ne_one : 0 ≠ (1:α))
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lemma zero_ne_one [s: zero_ne_one_class α] : 0 ≠ (1:α) :=
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@zero_ne_one_class.zero_ne_one α s
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/- semiring -/
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class semiring (α : Type u) extends add_comm_monoid α, monoid α, distrib α, mul_zero_class α
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section semiring
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variables [semiring α]
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lemma one_add_one_eq_two : 1 + 1 = (2 : α) :=
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begin unfold bit0, reflexivity end
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lemma ne_zero_of_mul_ne_zero_right {a b : α} (h : a * b ≠ 0) : a ≠ 0 :=
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suppose a = 0,
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have a * b = 0, by rw [this, zero_mul],
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h this
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lemma ne_zero_of_mul_ne_zero_left {a b : α} (h : a * b ≠ 0) : b ≠ 0 :=
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suppose b = 0,
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have a * b = 0, by rw [this, mul_zero],
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h this
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lemma distrib_three_right (a b c d : α) : (a + b + c) * d = a * d + b * d + c * d :=
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by simp [right_distrib]
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end semiring
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class comm_semiring (α : Type u) extends semiring α, comm_monoid α
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/- ring -/
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class ring (α : Type u) extends add_comm_group α, monoid α, distrib α
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lemma ring.mul_zero [ring α] (a : α) : a * 0 = 0 :=
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have a * 0 + 0 = a * 0 + a * 0, from calc
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a * 0 + 0 = a * (0 + 0) : by simp
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... = a * 0 + a * 0 : by rw left_distrib,
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show a * 0 = 0, from (add_left_cancel this)^.symm
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lemma ring.zero_mul [ring α] (a : α) : 0 * a = 0 :=
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have 0 * a + 0 = 0 * a + 0 * a, from calc
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0 * a + 0 = (0 + 0) * a : by simp
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... = 0 * a + 0 * a : by rewrite right_distrib,
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show 0 * a = 0, from (add_left_cancel this)^.symm
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instance ring.to_semiring [s : ring α] : semiring α :=
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{ s with
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mul_zero := ring.mul_zero,
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zero_mul := ring.zero_mul }
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lemma neg_mul_eq_neg_mul [s : ring α] (a b : α) : -(a * b) = -a * b :=
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neg_eq_of_add_eq_zero
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begin rw [-right_distrib, add_right_neg, zero_mul] end
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lemma neg_mul_eq_mul_neg [s : ring α] (a b : α) : -(a * b) = a * -b :=
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neg_eq_of_add_eq_zero
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begin rw [-left_distrib, add_right_neg, mul_zero] end
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@[simp] lemma neg_mul_eq_neg_mul_symm [s : ring α] (a b : α) : - a * b = - (a * b) :=
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eq.symm (neg_mul_eq_neg_mul a b)
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@[simp] lemma mul_neg_eq_neg_mul_symm [s : ring α] (a b : α) : a * - b = - (a * b) :=
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eq.symm (neg_mul_eq_mul_neg a b)
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lemma neg_mul_neg [s : ring α] (a b : α) : -a * -b = a * b :=
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by simp
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lemma neg_mul_comm [s : ring α] (a b : α) : -a * b = a * -b :=
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by simp
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theorem neg_eq_neg_one_mul [s : ring α] (a : α) : -a = -1 * a :=
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by simp
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lemma mul_sub_left_distrib [s : ring α] (a b c : α) : a * (b - c) = a * b - a * c :=
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calc
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a * (b - c) = a * b + a * -c : left_distrib a b (-c)
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... = a * b - a * c : by simp
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def mul_sub := @mul_sub_left_distrib
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lemma mul_sub_right_distrib [s : ring α] (a b c : α) : (a - b) * c = a * c - b * c :=
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calc
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(a - b) * c = a * c + -b * c : right_distrib a (-b) c
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... = a * c - b * c : by simp
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def sub_mul := @mul_sub_right_distrib
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class comm_ring (α : Type u) extends ring α, comm_semigroup α
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instance comm_ring.to_comm_semiring [s : comm_ring α] : comm_semiring α :=
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{ s with
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mul_zero := mul_zero,
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zero_mul := zero_mul }
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section comm_ring
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variable [comm_ring α]
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lemma mul_self_sub_mul_self_eq (a b : α) : a * a - b * b = (a + b) * (a - b) :=
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by simp [right_distrib, left_distrib]
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lemma mul_self_sub_one_eq (a : α) : a * a - 1 = (a + 1) * (a - 1) :=
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by simp [right_distrib, left_distrib]
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lemma add_mul_self_eq (a b : α) : (a + b) * (a + b) = a*a + 2*a*b + b*b :=
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calc (a + b)*(a + b) = a*a + (1+1)*a*b + b*b : by simp [right_distrib, left_distrib]
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... = a*a + 2*a*b + b*b : by rw one_add_one_eq_two
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end comm_ring
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class no_zero_divisors (α : Type u) extends has_mul α, has_zero α :=
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(eq_zero_or_eq_zero_of_mul_eq_zero : ∀ a b : α, a * b = 0 → a = 0 ∨ b = 0)
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lemma eq_zero_or_eq_zero_of_mul_eq_zero [no_zero_divisors α] {a b : α} (h : a * b = 0) : a = 0 ∨ b = 0 :=
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no_zero_divisors.eq_zero_or_eq_zero_of_mul_eq_zero a b h
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lemma eq_zero_of_mul_self_eq_zero [no_zero_divisors α] {a : α} (h : a * a = 0) : a = 0 :=
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or.elim (eq_zero_or_eq_zero_of_mul_eq_zero h) (assume h', h') (assume h', h')
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class integral_domain (α : Type u) extends comm_ring α, no_zero_divisors α, zero_ne_one_class α
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section integral_domain
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variable [integral_domain α]
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lemma mul_ne_zero {a b : α} (h₁ : a ≠ 0) (h₂ : b ≠ 0) : a * b ≠ 0 :=
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λ h, or.elim (eq_zero_or_eq_zero_of_mul_eq_zero h) (assume h₃, h₁ h₃) (assume h₄, h₂ h₄)
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lemma eq_of_mul_eq_mul_right {a b c : α} (ha : a ≠ 0) (h : b * a = c * a) : b = c :=
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have b * a - c * a = 0, from sub_eq_zero_of_eq h,
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have (b - c) * a = 0, by rw [mul_sub_right_distrib, this],
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have b - c = 0, from (eq_zero_or_eq_zero_of_mul_eq_zero this)^.resolve_right ha,
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eq_of_sub_eq_zero this
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lemma eq_of_mul_eq_mul_left {a b c : α} (ha : a ≠ 0) (h : a * b = a * c) : b = c :=
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have a * b - a * c = 0, from sub_eq_zero_of_eq h,
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have a * (b - c) = 0, by rw [mul_sub_left_distrib, this],
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have b - c = 0, from (eq_zero_or_eq_zero_of_mul_eq_zero this)^.resolve_left ha,
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eq_of_sub_eq_zero this
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lemma eq_zero_of_mul_eq_self_right {a b : α} (h₁ : b ≠ 1) (h₂ : a * b = a) : a = 0 :=
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have hb : b - 1 ≠ 0, from
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suppose b - 1 = 0,
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have b = 0 + 1, from eq_add_of_sub_eq this,
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have b = 1, by rwa zero_add at this,
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h₁ this,
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have a * b - a = 0, by simp [h₂],
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have a * (b - 1) = 0, by rwa [mul_sub_left_distrib, mul_one],
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show a = 0, from (eq_zero_or_eq_zero_of_mul_eq_zero this)^.resolve_right hb
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lemma eq_zero_of_mul_eq_self_left {a b : α} (h₁ : b ≠ 1) (h₂ : b * a = a) : a = 0 :=
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eq_zero_of_mul_eq_self_right h₁ (by rwa mul_comm at h₂)
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lemma mul_self_eq_mul_self_iff (a b : α) : a * a = b * b ↔ a = b ∨ a = -b :=
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iff.intro
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(suppose a * a = b * b,
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have (a - b) * (a + b) = 0,
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by rewrite [mul_comm, -mul_self_sub_mul_self_eq, this, sub_self],
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have a - b = 0 ∨ a + b = 0, from eq_zero_or_eq_zero_of_mul_eq_zero this,
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or.elim this
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(suppose a - b = 0, or.inl (eq_of_sub_eq_zero this))
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(suppose a + b = 0, or.inr (eq_neg_of_add_eq_zero this)))
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(suppose a = b ∨ a = -b, or.elim this
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(suppose a = b, by rewrite this)
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(suppose a = -b, by rewrite [this, neg_mul_neg]))
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lemma mul_self_eq_one_iff (a : α) : a * a = 1 ↔ a = 1 ∨ a = -1 :=
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have a * a = 1 * 1 ↔ a = 1 ∨ a = -1, from mul_self_eq_mul_self_iff a 1,
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by rwa mul_one at this
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end integral_domain
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/- TODO(Leo): remove the following annotations as soon as we have support for arithmetic
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in the SMT tactic framework -/
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attribute [ematch] add_zero zero_add mul_one one_mul mul_zero zero_mul
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