theorem Th33:
  A in SF implies A is ManySortedSubset of M
proof
A1: SF c= bool M by PBOOLE:def 18;
  assume A in SF;
  then A in bool M by A1,PBOOLE:9;
  then A c= M by MBOOLEAN:18;
  hence thesis by PBOOLE:def 18;
end;
