Singular locus
Near we want to have the BRST transformation of the form:

This means that we should have action of the first order, and remember I also want holomorphic:

If we had action like then we would have something like which is not what we want! It is essential to have the action of the first order. In practice, the leading term comes out like ; to make it of the order we rewrite
The other fields are of the higher order:

with some quadratic form . For we need:

In the pure spinor formalism we put (the Gamma-matrices)