reserve a,b,c for set;

theorem Th16:
  card INT = omega
proof
A1: card INT c= card (NAT \/ [:{0},NAT:]) by CARD_1:11,NUMBERS:def 4;
A2: card [:NAT,{0}:] = card [:{0},NAT:] by CARD_2:4;
A3: card [:NAT,{0}:] = card NAT by CARD_1:69;
  omega+`(omega qua cardinal number) = omega by CARD_2:75;
  then card (NAT \/ [:{0},NAT:]) c= omega by A3,A2,CARD_2:34;
  hence card INT c= omega by A1;
  thus thesis by CARD_1:11,47,NUMBERS:17;
end;
