StateRuleSelection

"Rule Selection", the clause-resolution counterpart of StatePrimitiveSelection, and where several ISO special cases live: true/! succeed without touching the knowledge base at all (! additionally triggers cut, see below); fail/false, and goals that don't exist anywhere, move to StateBacktracking or StateException depending on the Unknown flag (error/fail/warning); the general case queries the static/dynamic knowledge bases and the libraries' own theories, freshCopy()s the matching clauses to rename variables apart, and moves to StateRuleExecution with the fresh rule stream as a new choice point.

The formal paper describes cut abstractly as "prune the choice-point queue up to the parent goal's choice point"; computeCutLimit/performCut implement something considerably more careful, because ISO cut semantics are subtler than that:

• Cut is transparent through conjunction, disjunction and if-then (the transparentToCut signatures) -- a cut inside a clause body's conjunction cuts choice points belonging to the clause, not to some imaginary choice point for the comma itself; computeCutLimit walks up through these control constructs to find the real enclosing procedure.

• Cut interacts with last-call optimization (isTailRecursive): a tail call to the same predicate reuses the current execution-context frame (replaceWithChildAppendingRulesAndChoicePoints) rather than growing the stack, an optimisation the formal model does not need to talk about since it treats the stack as unbounded.

• A MagicCut marker exists for cuts injected by other built-ins (e.g. once/1, if-then-else) that must cut back to the caller's choice point rather than the lexically enclosing clause, since those built-ins are themselves implemented as ordinary rules over this same state machine (see it.unibo.tuprolog.solve.classic.stdlib.rule).

None of this changes the shape of the FSM: cut is still handled here, still ends up at StateGoalSelection, still only manipulates the choice-point queue.