fact: Definition echelon_recdef c (p := erecdef_combine h1 h2 h3) := restr (graph (transfinite_defined Nat_order (fun u => (p (graph u) (P (Vg c (source u))) (Q (Vg c (source u))))))) (slength c).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq)