
theorem Th26:
  for L1,L2 be non empty RelStr st L1,L2 are_isomorphic holds card
  the carrier of L1 = card the carrier of L2
proof
  let L1,L2 be non empty RelStr;
  assume L1,L2 are_isomorphic;
  then consider f be Function of L1,L2 such that
A1: f is isomorphic by WAYBEL_1:def 8;
A2: dom f = the carrier of L1 by FUNCT_2:def 1;
  f is one-to-one & rng f = the carrier of L2 by A1,WAYBEL_0:66;
  then the carrier of L1,the carrier of L2 are_equipotent by A2,WELLORD2:def 4;
  hence thesis by CARD_1:5;
end;
