An Operational Calculus for the Mould Operad

The operad of moulds is realized in terms of an operational calculus of formal integrals (continuous formal power series). This leads to many simplifications and to the discovery of various suboperads. In particular, we prove a conjecture of the first author about the inverse image of noncrossing trees in the dendriform operad. Finally, we explain a connection with the formalism of noncommutative symmetric functions.