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

theorem Th15:
   for b be bag of 1 holds len (divisors b) = (b.0) + 1
   proof
     let b be bag of 1;
A1:  card dom(NBag1|(Segm ((b.0)+1))) = card rng(NBag1|(Segm ((b.0)+1)))
     by CARD_1:70;
     (b.0) + 1 = card{x where x is bag of 1 : x.0 <= b.0} by Th14,A1
     .= card rng(divisors b) by Th13 .= card dom (divisors b) by CARD_1:70
     .= card (Seg (len (divisors b))) by FINSEQ_1:def 3
     .= len (divisors b);
     hence thesis;
   end;
