Since the dimacs functor has an internal state (relating to the output
in iCNF format), it is desirable to have a generative functor, inc as
esomeone wants to output select parts of a problem to two distinct iCNF
files).
When adding clauses that conatins duplicates, the checking
of some proof would fail because there would sometime be multiple
littrals to resolve over. This fixes that problem.
When theory raises a conflict, it is analysed, and the backtracck clause
that result is added to the solver, however, I didn't find yet a
satisfying answer as to wether the original clause is implied (or not)
by this backtrack clause, so in order not to lose information, we also
add the original conflict clause when it comes from the theory (because
if not, then it comes from a conflict detected during propgation, so the
conflict clause is actually already attached).
In add_clause, a conflcit at level 0 raised Unsat, but was forgotten,
which is obviously incorrect as succesive solving of the same problem
would yield different results.
Indeed, the previous strategy was that late propagations didn't need to
be propagated since they already have been, however that may not be the
case as a conflict might arise during propagation. It manifested as a
bug when the conflict did *not* depend on local hyps, and was tragically
lost during popping.
In Plugin, and Theory, if_sat function now has the same type as assume
Additionally, some insertions into the heap have been moved to avoid
some unnecessary operations.
