11 lines
297 B
Text
11 lines
297 B
Text
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def head {α} : (as : List α) → as ≠ [] → α
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| [], h => absurd rfl h
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| a::as, _ => a
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theorem head_cons {α} (a : α) (as : List α) : head (a::as) (fun h => List.noConfusion h) = a :=
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rfl
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theorem head_cons' {α} (a : α) (as : List α) (h : a::as ≠ []) : head (a::as) h = a :=
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rfl
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