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

theorem
  X misses Y implies (X (\/) Y) (\) Y = X
proof
  (X (\/) Y) (\) Y = X (\) Y by Th75;
  hence thesis by Th115;
end;
