Let 
and 
be distinct trilinear points, neither lying on a sideline of 
. Then the crossdifference of 
and 
is the point 
defined by trilinears
 |
Treating 
and 
as vectors, the crossdifference is then simply given by 
.
It can be constructed as the isogonal conjugate of the trilinear pole of the line 
. Thus, 
is the crossdifference of 
and 
, and 
is the crossdifference of 
and 
.
