3ebce4e190
This PR completes alignment of `List.getLast`/`List.getLast!`/`List.getLast?` lemmas with the corresponding lemmas for Array and Vector.
59 lines
1.5 KiB
Text
59 lines
1.5 KiB
Text
/-
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Copyright (c) 2021 Eric Rodriguez. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Eric Rodriguez
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-/
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prelude
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import Init.Data.Zero
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/-!
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# `NeZero` typeclass
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We create a typeclass `NeZero n` which carries around the fact that `(n : R) ≠ 0`.
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## Main declarations
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* `NeZero`: `n ≠ 0` as a typeclass.
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-/
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variable {R : Type _} [Zero R]
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/-- A type-class version of `n ≠ 0`. -/
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class NeZero (n : R) : Prop where
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/-- The proposition that `n` is not zero. -/
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out : n ≠ 0
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theorem NeZero.ne (n : R) [h : NeZero n] : n ≠ 0 :=
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h.out
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theorem NeZero.ne' (n : R) [h : NeZero n] : 0 ≠ n :=
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h.out.symm
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theorem neZero_iff {n : R} : NeZero n ↔ n ≠ 0 :=
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⟨fun h ↦ h.out, NeZero.mk⟩
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@[simp] theorem neZero_zero_iff_false {α : Type _} [Zero α] : NeZero (0 : α) ↔ False :=
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⟨fun _ ↦ NeZero.ne (0 : α) rfl, fun h ↦ h.elim⟩
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instance {p : Prop} [Decidable p] {n m : Nat} [NeZero n] [NeZero m] :
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NeZero (if p then n else m) := by
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split <;> infer_instance
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instance {n m : Nat} [h : NeZero n] : NeZero (n + m) where
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out :=
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match n, h, m with
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| _ + 1, _, 0
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| _ + 1, _, _ + 1 => fun h => nomatch h
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instance {n m : Nat} [h : NeZero m] : NeZero (n + m) where
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out :=
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match m, h, n with
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| _ + 1, _, 0 => fun h => nomatch h
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| _ + 1, _, _ + 1 => fun h => nomatch h
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instance {n m : Nat} [hn : NeZero n] [hm : NeZero m] : NeZero (n * m) where
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out :=
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match n, hn, m, hm with
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| _ + 1, _, _ + 1, _ => fun h => nomatch h
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