reserve u,v,x,x1,x2,y,y1,y2,z,p,a for object,
        A,B,X,X1,X2,X3,X4,Y,Y1,Y2,Z,N,M for set;

theorem
  x <> y implies [:{x},X:] misses [:{y},Y:] & [:X,{x}:] misses [:Y,{y}:]
proof
  assume x<>y;
  then {x} misses {y} by Th11;
  hence thesis by Th103;
end;
