(** ** The heap property *)
Inductive is_heap : Tree -> Prop :=
| nil_is_heap : is_heap Tree_Leaf
| node_is_heap :
forall (a:A) (T1 T2:Tree),
leA_Tree a T1 ->
leA_Tree a T2 ->
is_heap T1 -> is_heap T2 -> is_heap (Tree_Node a T1 T2).
#[deprecated(since="8.3", note="Use mergesort.v")]

Lemma invert_heap :
forall (a:A) (T1 T2:Tree),
is_heap (Tree_Node a T1 T2) ->
leA_Tree a T1 /\ leA_Tree a T2 /\ is_heap T1 /\ is_heap T2.