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

theorem
  X (/\) Y misses X (\) Y
proof
  X (/\) Y c= Y & X (\) Y misses Y by Th15,Th108;
  hence thesis by Th107;
end;
