
theorem Th20:
  for M being finite-degree Matroid for C being finite Subset of M
  holds Rnk C <= card C
proof
  let M be finite-degree Matroid;
  let C be finite Subset of M;
  ex A being independent Subset of M st A c= C & card A = Rnk C by Th18;
  then Segm Rnk C c= Segm card C by CARD_1:11;
  hence thesis by NAT_1:39;
end;
