reserve x,x1,x2,y,y9,y1,y2,z,z1,z2 for object,P,X,X1,X2,Y,Y1,Y2,V,Z for set;

theorem
  for f being Function holds f|X tolerates f
proof
  let f be Function;
  (f|X) c= f by RELAT_1:59;
  hence thesis by Th52;
end;
