  We consider the horocyclic flow corresponding to a (topologically mixing)
Anosov flow or diffeomorphism, and establish the uniqueness of transverse
quasi-invariant measures with H\"older Jacobians. In the same setting, we give
a precise characterization of the equilibrium states of the hyperbolic system,
showing that existence of a family of Radon measures on the horocyclic
foliation such that any probability (invariant or not) having conditionals
given by this family, necessarily is the unique equilibrium state of the
system.
