proposition: Lemma inl_prop2 S i j k: gle (isr S) i j -> gle (isr S) j k -> Vg (isf S) (J j k) \coP Vg (isf S) (J i j).
proof: Proof. rewrite /composable. by move => /is_function_f [fa sa ->] /is_function_f [fb -> tb]; aw. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)