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

theorem
  X c= Y & X c= Z & Y misses Z implies X = EmptyMS I
proof
  assume
A1: X c= Y & X c= Z;
  assume Y misses Z;
  then Y (/\) Z = EmptyMS I by Th111;
  hence thesis by A1,Th17,Th44;
end;
