Vertical Representation of C∞-words

International audience; We present a new framework for dealing with C∞-words, based on their left and right frontiers. Thisallows us to give a compact representation of them, and to describe the set of C∞-words throughan infinite directed acyclic graph G. This graph is defined by a map acting on the frontiers ofC∞-words. We show that this map can be defined recursively and with no explicit reference toC∞-words. We then show that some important conjectures on C∞-words follow from analogousstatements on the structure of the graph G.