theorem Th6:
  for T being set, F being Subset-Family of T holds F <> {}
  implies meet COMPLEMENT(F) = (union F)`
proof
  let T be set, F be Subset-Family of T;
  assume F <> {};
  then meet COMPLEMENT(F) = [#]T \ union F by SETFAM_1:33;
  hence thesis;
end;
