As mentioned earlier, an agent is modeled as a population of profiles. The structure of an individual profile is described in the preceding sections. The rest of this chapter describes the population characteristics and behavior in response to changing user interests.
The formal definition of a Population is given in equation 
It is defined as a set, where each element of the set is a pair of profile and
its fitness.
The profile representation is the same as described in Section ,
which is repeated here for convenience.
where i = a(uthors), k(eywords), l(ocations), n(ewsgroups),
p(riority), s(ource), etc.
The genetic operators, namely crossover and mutation, refresh the population every generation by introducing new members into the population and flushing out the unfit ones.