31 lines
845 B
Text
31 lines
845 B
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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Author: Leonardo de Moura
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-/
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prelude
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import init.nat
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open nat
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structure fin (n : nat) := (val : nat) (is_lt : val < n)
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namespace fin
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variable {n : nat}
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lemma eq_of_veq : ∀ {i j : fin n}, (val i) = (val j) → i = j
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| ⟨iv, ilt₁⟩ ⟨.iv, ilt₂⟩ rfl := rfl
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lemma veq_of_eq : ∀ {i j : fin n}, i = j → (val i) = (val j)
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| ⟨iv, ilt⟩ .⟨iv, ilt⟩ rfl := rfl
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end fin
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open fin
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attribute [instance]
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protected definition fin.has_decidable_eq (n : nat) : ∀ (i j : fin n), decidable (i = j)
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| ⟨ival, ilt⟩ ⟨jval, jlt⟩ :=
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match nat.has_decidable_eq ival jval with
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| is_true h₁ := is_true (eq_of_veq h₁)
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| is_false h₁ := is_false (λ h₂, absurd (veq_of_eq h₂) h₁)
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end
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