theorem Th34:
  x*y = y*x
   proof
     consider a such that
A1:  x = Class(EqRel(S),a) by Th32;
     consider b such that
A2:  y = Class(EqRel(S),b) by Th32;
     x*y = Class(EqRel(S),a*b) by A1,A2,Th33
     .= Class(EqRel(S),b*a)  .= y*x by A1,A2,Th33;
     hence thesis;
   end;
