PCThread2 fully functional
I think there should be a way to get it faster by using a better
formulation in the if-statements and by using the equivalence-classes as
in the first algorithm. Also there's a possibility to get rid of the
functions without the last element because |\mathcal{A}_n| =
|\mathcal{A}_{n-1} + \sum_{\alpha, \beta, \gamma \leq \rho \in
\mathcal{A}_n \setminus \mathcal{A}_{n-1}} |[\bot, \alpha \wedge \beta
\wedge \gamma]||[\alpha \vee \beta, \rho]||[\alpha \vee \gamma,
\rho]||[\beta \vee \gamma, \rho]|.