Published online by Cambridge University Press: 22 April 2019
We study continuous countably (strictly) monotone maps defined on a tame graph, i.e. a special Peano continuum for which the set containing branch points and end points has countable closure. In our investigation we confine ourselves to the countable Markov case. We show a necessary and sufficient condition under which a locally eventually onto, countably Markov map $f$ of a tame graph
$G$ is conjugate to a map
$g$ of constant slope. In particular, we show that in the case of a Markov map
$f$ that corresponds to a recurrent transition matrix, the condition is satisfied for a constant slope
$e^{h_{\text{top}}(f)}$, where
$h_{\text{top}}(f)$ is the topological entropy of
$f$. Moreover, we show that in our class the topological entropy
$h_{\text{top}}(f)$ is achievable through horseshoes of the map
$f$.