is the origin and that
. There is no loss of generality
if we assume that
is the origin and that
.
Therefore, we seek the 
such that 
with 
non-zero. Since the hyperbolic inner product (6.1) is non-degenerate,
this is just the kernel of the functional 
,
or
|
|
that is, the events 
such that
|
|
The result is immediate.
,
.