11 lines
258 B
Text
11 lines
258 B
Text
import data.nat
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using nat
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inductive list (T : Type) : Type :=
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| nil {} : list T
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| cons : T → list T → list T
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definition length {T : Type} : list T → nat := list_rec 0 (fun x l m, succ m)
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theorem length_nil {T : Type} : length (@nil T) = 0
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:= refl _
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