N-string vertex, canonical forms and bosonization

We give the field representation of the canonical forms for the operators which generate the projective transformation. This representation is also applicable in formulating the N-string vertex of Lovelace and Olive. It shows that they have the properties of a transition operator. Requiring the same properties for the ghost sector in bosonized form we construct the BRST invariant canonical form and the N-string vertex. We consider the (N - 3) b-ghost insertion. We show that the resulting vertex with (N - 3) parameters corresponding to the location of the ghosts is symmetric with respect to the N strings and it gives the proper integration measure.