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)