theorem
  0 < m & m*n divides m implies n = 1
  proof
    assume that
A1: 0 < m and
A2: m*n divides m;
    m divides m*n;
    then m = m*n or m = -m*n by A2,INT_2:11;
    hence n = 1 by A1,XCMPLX_1:7;
  end;
