fact: Record wf_num e := WfNum { wf_num0 : forall x, (num e x == 0) = (x \in white e); wf_num_infty : forall x, (num e x == infty) = (x \in cover (esccs e)); wf_num_lt : forall x, num e x != infty -> num e x < sn e; wf_sn : sn e = #|gray e :|: black e|.+1; wf_num_stack : {in stack e &, forall x y, (num e x <= num e y) = (y <[e]= x)} }.
imports: mathcomp(all_ssreflect) bigmin extra