theorem
  for G being loopless _Graph, H being Subgraph of G
  holds H.tChromaticNum() c= G.tChromaticNum()
proof
  let G be loopless _Graph, H be Subgraph of G;
  G is G.tChromaticNum()-tcolorable by Th186;
  hence thesis by Th189;
end;
