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

theorem
  (X (/\) Y) (\/) (X (/\) Z) = X implies X c= Y (\/) Z
proof
  assume (X (/\) Y) (\/) (X (/\) Z) = X;
  then X = X (/\) (Y (\/) Z) by Th32;
  hence thesis by Th15;
end;
