reserve T for non empty RelStr,
  A,B for Subset of T,
  x,x2,y,z for Element of T;

theorem Th5:
  A c= B implies A^f c= B^f
proof
  assume
A1: A c= B;
  let z be object;
  assume z in A^f;
  then ex y st y in A & z in U_FT y by FIN_TOPO:11;
  hence thesis by A1,FIN_TOPO:11;
end;
