We have,in this case,a spatial representation of the relations:
aXa + b, bZa+ b


and of Ar OO.
This furnishes us with a clear instance of the basic duality of
logistie formulae and we can already perceive its connexion with geo
metrical fundamental (planimetrical) duality,expressed by the fact


that the two straight lines a and b determine the point (a + b),while
the two points a and b determine the straight line ab. We thus see here
an absolute correspondence between the two operations of logic (addition
and multiplication) and the two operations of projective geometry (sec
tion and projection).
