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
  now
    let i be object;
    assume i in I;
    then (X (/\) Y).i = X.i /\ Y.i & (X (\+\) Y).i = X.i \+\ Y.i by Def5,Th4;
    hence (X (/\) Y).i misses (X (\+\) Y).i by XBOOLE_1:103;
  end;
  hence thesis;
end;
