theorem Th21:
  Domin_0(n,m) c= Choose(n,m,1,0)
proof
  let x be object;
  assume x in Domin_0(n,m);
  then consider p such that
A1: p = x and
A2: p is dominated_by_0 and
A3: dom p = n & Sum p = m by Def2;
  rng p c= {0,1} by A2;
  hence thesis by A1,A3,CARD_FIN:40;
end;
