(* * Copyright (c) 2009-2010, Andrew Appel, Robert Dockins and Aquinas Hobor. * *)
Definition constructive_join_sub {A} {JOIN: Join A} (w1 w3: A) := {w2 | join w1 w2 w3}.

Lemma cjoin_sub_join_sub{A} {JOIN: Join A}:
forall {w1 w3}, constructive_join_sub w1 w3 -> join_sub w1 w3.