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Ce travail consiste à étudier les comportements des marches sur les arbres homogènes suivant la suite engendrée par une substitution. Dans la première partie, on étudie d’abord les marches sans orientation sur $\mathbb{Z}$ et on détermine complètement, d’après les propriétés combinatoires de la substitution, les conditions assurant que les marches sont bornées, récurrentes ou transientes. Comme corollaire, on obtient le comportement asymptotique des sommes partielles des coefficients de la suite substitutive....

Let $\varphi$ be a substitution over a 2-letter alphabet, say $\{a,b\}$. If $\varphi \left(a\right)$ and $\varphi \left(b\right)$ begin with $a$ and $b$ respectively, $\varphi$ has two fixed points beginning with $a$ and $b$ respectively. We characterize substitutions with two cofinal fixed points (i.e., which differ only by prefixes). The proof is a combinatorial one, based on the study of repetitions of words in the fixed points.

Let $ϵ=({ϵ}_n{)}_{n\ge 0}$ be the Thue-Morse sequence, i.e., the sequence defined by the recurrence equations: $${ϵ}_0=1,{ϵ}_{2n}={ϵ}_n,{ϵ}_{2n+1}=1-{ϵ}_n.$$ We consider $\left\{\right|{ℰ}_n^p|{\}}_{n\ge 1,p\ge 0}$, the double sequence of Hankel determinants (modulo 2) associated with the Thue-Morse sequence. Together with three other sequences, it obeys a set of sixteen recurrence equations. It is shown to be automatic. Applications are given, namely to combinatorial properties of the Thue-Morse sequence and to the existence of certain Padé approximants of the power series ${\sum }_{n\ge 0}(-1{)}^{{ϵ}_n}{x}^n$.