16429e393d
It has been reported in the general channel that this example generates problems for the Lean 3 elaborator.
13 lines
290 B
Text
13 lines
290 B
Text
def Hd : List α → Type
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| [] => Unit
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| a :: _ => α
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def hd : (as : List α) → Hd as
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| [] => ()
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| a :: l => a
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theorem inj_hd : (a a': α) → (l l' : List α) → a :: l = a' :: l' → a = a' := by
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intro a a' l l' h
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show hd (a :: l) = hd (a' :: l')
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cases h
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rfl
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