  Pure spinor cohomology has been used to describe maximally supersymmetric
theories, like D=10 super-Yang-Mills and D=11 supergravity. Supersymmetry
closes on-shell in such theories, and the fields in the cohomology
automatically satisfy the equations of motion. In this paper, we investigate
the corresponding structure in a model with off-shell supersymmetry, N=1
super-Yang-Mills theory in D=6. Here, fields and antifields are obtained as
cohomologies in different complexes with respect to the BRST operator Q. It
turns out to be natural to enlarge the pure spinor space with additional
bosonic variables, subject to some constraints generalising the pure spinor
condition, in order to accommodate the different supermultiplets in the same
generalised pure spinor wave-function. We construct another BRST operator, s,
acting in the cohomology of Q, whose cohomology implies the equations of
motion. We comment on the possible use of similar approaches in other models.
