fact: Definition Typ_concg (x:Set) A S s y f R := let s' := Lg (domain S) (fun i => Vf (echelon_can_extension (Vg S i) (Typ_with_id f A)) (Vg s i)) in R x s <-> R y s'.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq)