7.2.5
The data set 
in (7.20) may be very large because there are
a combinatorial number of possible configurations in 
. In principle, all 
should be considered. However, we
assume that the configurations which are neighboring 
have the
largest influence on the selection of 
. Define the neighborhood
of 
as
where 
reads ``exists one and only one'' and 
is the
set of admissible labels for every 
. The 
consists of
all 
that differ from 
by one and only one component. This
confinement reduces the search space to an enormous extent. After the
configuration space is confined to 
, the set of training data
is computed as
which is much smaller than the 
in Eq.(7.20).
