Ward identities for Lagrangian conformal models

Some aspects of conformal theories with Lagrangian representation, are discussed. The study is carried out in the framework of formal perturbative series. The development of the concepts and the problems raised, are illustrated by the free bosonic string. The association of the Slavnov symmetry with diffeomorphisms is underlined. The problems involving the construction of a renormalized perturbation theory, are discussed. Studies requiring further and accurate investigations, are presented