inductive BST.{u_1} : {β : Type u_1} → Tree β → Prop
number of parameters: 1
constructors:
BST.leaf : ∀ {β : Type u_1}, BST Tree.leaf
BST.node : ∀ {β : Type u_1} {key : Nat} {left right : Tree β} {value : β},
  ForallTree (fun k v => k < key) left →
    ForallTree (fun k v => key < k) right → BST left → BST right → BST (left.node key value right)