11 lines
284 B
Text
11 lines
284 B
Text
reset_grind_attrs%
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open List
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attribute [grind] List.map_nil
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theorem map_eq_cons_iff {f : α → β} {l : List α} :
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map f l = b :: l₂ ↔ ∃ a l₁, l = a :: l₁ ∧ f a = b ∧ map f l₁ = l₂ := by
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cases l
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case nil => grind -- kernel error
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case cons a l => sorry
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