reserve Q,Q1,Q2 for multLoop;
reserve x,y,z,w,u,v for Element of Q;

theorem Th10:
  K_op(x,y) = 1.Q implies x*y = y*x
proof
  assume K_op(x,y) = 1.Q;
  then (y*x) * 1.Q = x*y;
  hence thesis;
end;
