proposition: Lemma tseq_connect_before (g : V -> seq V) x y : acyclic (grel g) -> connect (grel g) x y -> before (tseq g) x y.
proof: Proof. move=> acycg; have [sorted all] := tseq_correct g. by apply: acyclic_connect_before. Qed.
imports: mathcomp(all_ssreflect) extra acyclic kosaraju