 reserve I for non empty set;
 reserve i for Element of I;
 reserve F for Group-Family of I;
 reserve G for Group;

theorem Th9:
  (Carrier F).i = the carrier of F.i
proof
  ex R being 1-sorted st R = F.i & (Carrier F).i = the carrier of R
  by PRALG_1:def 15;
  hence thesis;
end;
