theorem Th39:
  A c= M & B c= M implies {A,B} is MSSubsetFamily of M
proof
  assume A c= M & B c= M;
  then {A} is MSSubsetFamily of M & {B} is MSSubsetFamily of M by Th38;
  then {A} (\/) {B} is MSSubsetFamily of M by Th34;
  hence thesis by PZFMISC1:10;
end;
