29 lines
586 B
Text
29 lines
586 B
Text
open nat
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inductive tree (A : Type) :=
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leaf : A → tree A,
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node : tree_list A → tree A
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with tree_list :=
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nil : tree_list A,
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cons : tree A → tree_list A → tree_list A
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namespace tree_list
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definition len {A : Type} : tree_list A → nat,
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len (nil A) := 0,
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len (cons t l) := len l + 1
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theorem len_nil {A : Type} : len (nil A) = 0 :=
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rfl
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theorem len_cons {A : Type} (t : tree A) (l : tree_list A) : len (cons t l) = len l + 1 :=
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rfl
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variables (A : Type) (t1 t2 t3 : tree A)
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example : len (cons t1 (cons t2 (cons t3 (nil A)))) = 3 :=
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rfl
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print definition len
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end tree_list
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