15 lines
319 B
Text
15 lines
319 B
Text
open nat
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inductive tree (A : Type)
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| leaf : A → tree
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| node : tree → tree → tree
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check tree.node
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definition size {A : Type} (t : tree A) : nat :=
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tree.rec (λ a, 1) (λ t₁ t₂ n₁ n₂, n₁ + n₂) t
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check size
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eval size (tree.node (tree.node (tree.leaf 0) (tree.leaf 1))
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(tree.leaf 0))
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