For any C1 expanding map f of the circle we study the equilibrium states for
the potential -log |f'|. We formulate a C1 generalization of Pesin's Entropy
Formula that holds for all the SRB measures if they exist, and for all the
(necessarily existing) SRB-like measures. In the C1-generic case Pesin's
Entropy Formula holds for a unique SRB measure which is not absolutely
continuous with respect to Lebesgue. The result also stands in the non generic
case for which no SRB measure exists.Comment: Un this version we include some addings and corrections that were
suggested by the referees. The final version will appear in Portugaliae
Mathematica and will be available at
http://www.ems-ph.org/journals/journal.php?jrn=p
