A Graded M\"obius transform and its harmonic interpretation

We give a graded version of the M"obius inversion formula in the framework of trace monoids. The formula is based on a graded version of the M"obius transform, related to the notion of height deriving from the Cartier-Foata normal form of the elements of a trace monoid. Using the notion of Bernoulli measures on the boundary of a trace monoid developped recently, we study a probabilistic interpretation of the graded inversion formula. We introduce M"obius harmonic functions for trace monoids and obtain an integral representation formula for them, analogous to the Poisson formula for harmonic functions associated to random walks on trees.