  We give an alternative proof of a conjecture of Bollob\'as, Brightwell and
Leader, first proved by Peter Allen, stating that the number of boolean
functions definable by 2-SAT formulae is $(1+o(1))2^{\binom{n+1}{2}}$. One step
in the proof determines the asymptotics of the number of
"odd-blue-triangle-free" graphs on $n$ vertices.
