theorem Th26:
  Cl Int T = Cl Int Cl Int T
proof
  Int Int T c= Int Cl Int T by Th19,PRE_TOPC:18;
  then
A1: Cl Int T c= Cl Int Cl Int T by PRE_TOPC:19;
  Cl Int Cl Int T c= Cl Cl Int T by Th16,PRE_TOPC:19;
  hence thesis by A1;
end;
