(* * 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 constructive_join_sub_refl {A} `{Perm_alg A}{SA: Sep_alg A}: forall x, constructive_join_sub x x.