
theorem Th2: :: ssf0:
for X, Y being set, F being Subset-Family of X, G being Subset-Family of Y
 holds F \/ G is Subset-Family of X \/ Y
proof
 let X, Y be set, F be Subset-Family of X, G be Subset-Family of Y;
A1: F \/ G c= bool X \/ bool Y by XBOOLE_1:13;
   bool X \/ bool Y c= bool (X \/ Y) by ZFMISC_1:69;
  hence F \/ G is Subset-Family of X \/ Y by A1,XBOOLE_1:1;
end;
