  Vertex operators in string theory come in two varieties: integrated and
unintegrated. Understanding both types is important for the calculation of the
string theory amplitudes. The relation between them is a descent procedure
typically involving the b-ghost. In the pure spinor formalism vertex operators
can be identified as cohomology classes of an infinite-dimensional Lie
superalgebra formed by covariant derivatives. We show that in this language the
construction of the integrated vertex from an unintegrated vertex is very
straightforward, and amounts to the evaluation of the cocycle on the
generalized Lax currents.
