“…In [54], Zhang introduced a new version of Bowen's equation which involves the limit of a sequence of topological pressures for singular valued potentials, and proved that the unique solution of this equation is an upper bound of the Hausdorff dimension of repellers. Finally, in [2], using thermodynamic formalism for sub-additive potentials developed in [12], the authors showed that the zero of the topological pressure of sub-additive singular valued potentials Φ f (t) = {−ϕ t (·, f n )} n≥1 (see precise definition in Section 3.1) gives an upper bound of the Hausdorff dimension of repellers, and furthermore, that the upper bounds obtained in the previous works [2,19,54] are all equal. We refer the reader to [14] and [7] for a detailed description of the recent progress in dimension theory of dynamical systems.…”