
theorem Th21:
  for G1 being _finite Tree-like _Graph
  for G2 being spanning Tree-like Subgraph of G1
  holds G1 == G2
proof
  let G1 be _finite Tree-like _Graph, G2 be spanning Tree-like Subgraph of G1;
  G1.order() = G2.order() by GLIB_000:117;
  then G1.size() + 1 = G2.order() by GLIB_002:47;
  then G1.size() + 1 = G2.size() + 1 by GLIB_002:47;
  hence thesis by GLIB_000:119;
end;
