reserve a,b for object, I,J for set;

theorem Th3:
  for N being multLoopStr, M being RelExtension of N holds 1.N = 1.M
  proof
    let N be multLoopStr;
    let M be RelExtension of N;
    the multLoopStr of N = the multLoopStr of M by RE;
    hence thesis;
  end;
