  Time evolution of the classification scheme generated by the EqRank algorithm
is studied with hep-th citation graph as an example. Intuitive expectations
about evolution of an adequate classification scheme for a growing set of
objects are formulated. Evolution compliant with these expectations is called
natural. It is demonstrated that EqRank yields a naturally evolving
classification scheme. We conclude that EqRank can be used as a means to detect
new scientific themes, and to track their development.
