 reserve o,o1,o2 for object;
 reserve n for Ordinal;
 reserve R,L for non degenerated comRing;
 reserve b for bag of 1;

theorem Th4:
    for b be bag of 1 holds dom b = {0} & rng b = {b.0}
    proof
      let b be bag of 1;
      dom b = {0} by CARD_1:49,PARTFUN1:def 2;
      hence thesis by FUNCT_1:4;
    end;
