The *duality* that exist between points and lines in
exist between points and planes in
. Thus a plane is
defined as a 4-tuple
and the equation of
this plane is given as

Analogous to the line at infinity (
) in
we have the *plane at infinity* (
) in
whose representation is
.

**Subsections**

Subhashis Banerjee
2008-01-20