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In this paper, we prove that infinite cancellative finitely generated hyperbolic monoids never contain N N as a submonoid but that they contain an element of infinite order and, if they are elementary, then they also contain a free monoid of rank at least 2. As a corollary we obtain that the latter have exponential growth. We prove these results by analysing the monoid of self-embeddings of hyperbolic digraphs and proving fixed-point theorems for them.
Matthias Hamann (Tue,) studied this question.