In this paper, we first recall some basic results about molecular expansions. In particular, we give some examples of molecular expansions, namely for the species of "Rooted trees" and of "Husimi graphs", weighted by their block-size distribution. We also describe briefly the addition formulas for the basic species which are essential for the recursive computation of molecular expansions.

Subsequently, we give a detailed description of the package
*Devmol*, and we conclude with two examples of applications,
to rooted trees weighted by a leaf counter and to connected graphs,
all of whose blocks are in a given family **B** of species of cyclo-set
type.

Received: April 16, 2003. Revised: July 18, 2003. Accepted: October 15, 2003.

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