let M be finite-degree Matroid; :: thesis: for C being finite Subset of holds
( C is independent iff card C = Rnk C )
let C be finite Subset of ; :: thesis: ( C is independent iff card C = Rnk C )
set X = { (card A) where A is independent Subset of : A c= C } ;

hereby :: thesis: ( card C = Rnk C implies C is independent )

assume C is independent ; :: thesis: card C = Rnk C
then card C in { (card A) where A is independent Subset of : A c= C } ;
then card C c= Rnk C by ZFMISC_1:92;
then A1: card C <= Rnk C by NAT_1:40;
Rnk C <= card C by Th20;
hence card C = Rnk C by A1, XXREAL_0:1; :: thesis: verum

end;

ex A being independent Subset of st
( A c= C & card A = Rnk C ) by Th18;
hence ( card C = Rnk C implies C is independent ) by CARD_FIN:1; :: thesis: verum