reserve A,B,C for Ordinal,
  X,X1,Y,Y1,Z for set,a,b,b1,b2,x,y,z for object,
  R for Relation,
  f,g,h for Function,
  k,m,n for Nat;
reserve M,N for Cardinal;

theorem Th7:
  card A c= A
proof
  ( ex B st card A = B & for C st C,B are_equipotent holds B c= C)& A,card
  A are_equipotent by Def1,Def2;
  hence thesis;
end;
