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[codex] rcases の rfl パターンを紹介 #2349

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[codex] rcases の rfl パターンを紹介 #2349

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14 changes: 14 additions & 0 deletions LeanByExample/Tactic/Rcases.lean
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Expand Up @@ -44,3 +44,17 @@ example (s : Sample) : True := by
guard_hyp z : String

trivial

/- ## 等式を rfl で分解する

`rcases` のパターンには `rfl` も使えます。等式の仮定 `h : a = b` に対して `rcases h with rfl` と書くと、`a` と `b` が同じ値である場合に分解されます。-/

example {a b c : Nat} (h : a = b) : a + c = b + c := by
rcases h with rfl
rfl

/- `rfl` は、ほかの `rcases` パターンの中にも書くことができます。たとえば、論理積を分解しながら、片方の等式を同時に消去できます。-/

example {a b : Nat} (h : a = b ∧ b = 3) : a = 3 := by
rcases h with ⟨rfl, hb⟩
exact hb
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