theorem Th8: :: MSSUBFAM:39
  A c= M & B c= M implies {A,B} is SubsetFamily of M
proof
  assume A c= M & B c= M;
  then {A} is SubsetFamily of M & {B} is SubsetFamily of M by Th7;
  then {A} \/ {B} is SubsetFamily of M by Th3;
  hence thesis by ENUMSET1:1;
end;
