reserve X,Y,Z,x,y,y1,y2 for set,
  D for non empty set,
  k,n,n1,n2,m2,m1 for Nat,

  L,K,M,N for Cardinal,
  f,g for Function;
reserve r for Real;
reserve p,q for FinSequence,
  k,m,n,n1,n2,n3 for Nat;
reserve f,f1,f2 for Function,
  X1,X2 for set;

theorem Th21:
  not X is finite implies card X = (omega)*`card X
proof
  assume
A1: not X is finite;
  then omega c= card X by CARD_3:85;
  hence thesis by A1,Th16;
end;
