Missing from a previous commit (selecting negation disjunct).
Experiments in the main algorithm (initstep behavior, renaming variables), will be cleaned up later.
Different order of variables in `when` clause guards.
Numerical abduction: only substitute out universal variables if atoms would conflict with the quantifier. Prune a branch with a contradictory premise, including conclusions of branches with premises subsumed by the premise considered (Important for premises with opti / subopti atoms, where some cases of the corresponding DNF would be "dead code".) Regression: binary increment.