Integrated vertex = deformation of the action
Suppose that we infinitesimally deformed the solution of the Master Equation by adding to it
some integrated vertex operator 
:
In order for this to satisfy the Master Equation to the first order in 
we require:
we require:
as we deform
, what should we do with
?
The answer is simple if satisfies the Siegel gauge:
satisfies the Siegel gauge:
In this case remains undeformed.
remains undeformed.On the next page we will explain what happens when Eq. (3) is not satisfied.