fact: Definition inl_equiv_rel S x y:= exists k, [/\ gle (isr S) (Q x) k, gle (isr S) (Q y) k & Vf (Vg (isf S) (J (Q x) k)) (P x) = Vf (Vg (isf S) (J (Q y) k)) (P y) ].
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)