reserve G, G1, G2 for _Graph, H for Subgraph of G;

theorem Th85:
  H.allForests() c= G.allForests()
proof
  now
    let x be object;
    assume x in H.allForests();
    then reconsider H9 = x as plain acyclic Subgraph of H by Th78;
    H9 is Subgraph of G by GLIB_000:43;
    hence x in G.allForests() by Th78;
  end;
  hence thesis by TARSKI:def 3;
end;
