reserve i,j,e,u for object;
reserve I for set; 
reserve x,X,Y,Z,V for ManySortedSet of I;
reserve I for non empty set,
  x,X,Y for ManySortedSet of I;

theorem Th124:
  not ex x st x in EmptyMS I
proof
  set i = the Element of I;
  given x such that
A1: x in EmptyMS I;
  x.i in EmptyMS I.i by A1;
  hence contradiction;
end;
