reserve U for Universe;
reserve x for Element of U;
reserve U1,U2 for Universe;

theorem Th55:
  for o,m being Element of U holds 1Cat(o,m) is U-element
  proof
    let o,m be Element of U;
    1Cat(o ,m)  = CatStr(# { o },{ m },  m :-> o , m :-> o,(m,m):->m #)
      by CAT_1:def 11;
    hence thesis;
  end;
