theorem Th189:
  G is c-tcolorable implies G.tChromaticNum() c= c
proof
  assume A1: G is c-tcolorable;
  per cases;
  suppose not G.order()+`G.size() in c;
    then c c= G.order()+`G.size() by ORDINAL1:16;
    then c in TColSet(G) by A1;
    hence thesis by SETFAM_1:3;
  end;
  suppose G.order()+`G.size() in c;
    then G.tChromaticNum() in c by Th188, ORDINAL1:12;
    hence thesis by ORDINAL1:def 2;
  end;
end;
