theorem Th38:
  M is measurable implies M is limit_cardinal
proof
  assume M is measurable;
  then consider F being Filter of M such that
A1: F is_complete_with M and
A2: F is non principal being_ultrafilter;
  assume
A3: not M is limit_cardinal;
  F is_complete_with card M by A1;
  hence contradiction by A2,A3,Th23,Th37;
end;
