lean2/tests/lean/run/forest2.lean

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import data.prod data.unit
open prod
inductive tree (A : Type) : Type :=
node : A → forest A → tree A
with forest : Type :=
nil : forest A,
cons : tree A → forest A → forest A
namespace solution1
inductive tree_forest (A : Type) :=
of_tree : tree A → tree_forest A,
of_forest : forest A → tree_forest A
inductive same_kind {A : Type} : tree_forest A → tree_forest A → Type :=
is_tree : Π (t₁ t₂ : tree A), same_kind (tree_forest.of_tree t₁) (tree_forest.of_tree t₂),
is_forest : Π (f₁ f₂ : forest A), same_kind (tree_forest.of_forest f₁) (tree_forest.of_forest f₂)
definition to_tree {A : Type} (tf : tree_forest A) (t : tree A) : same_kind tf (tree_forest.of_tree t) → tree A :=
tree_forest.cases_on tf
(λ t₁ H, t₁)
(λ f₁ H, by cases H)
end solution1
namespace solution2
variables {A B : Type}
inductive same_kind : sum A B → sum A B → Prop :=
isl : Π (a₁ a₂ : A), same_kind (sum.inl a₁) (sum.inl a₂),
isr : Π (b₁ b₂ : B), same_kind (sum.inr b₁) (sum.inr b₂)
definition to_left (s : sum A B) (a : A) : same_kind s (sum.inl a) → A :=
sum.cases_on s
(λ a₁ H, a₁)
(λ b₁ H, false.rec _ (by cases H))
definition to_right (s : sum A B) (b : B) : same_kind s (sum.inr b) → B :=
sum.cases_on s
(λ a₁ H, false.rec _ (by cases H))
(λ b₁ H, b₁)
theorem to_left_inl (a₁ a₂ : A) (H : same_kind (sum.intro_left B a₁) (sum.inl a₂)) : to_left (sum.inl a₁) a₂ H = a₁ :=
rfl
theorem to_right_inr (b₁ b₂ : B) (H : same_kind (sum.intro_right A b₁) (sum.inr b₂)) : to_right (sum.inr b₁) b₂ H = b₁ :=
rfl
end solution2