
 
returns true iff the $$xcoordinate of $$p is smaller than the $$xcoordinate of $$q or if the are the same and the $$ycoordinate of $$p is smaller than the $$ycoordinate of $$q, or, if both $$x and $$y coordinate are identical and the $$zcoordinate of $$p is smaller than the $$zcoordinate of $$q. 