Currently we copy all predicates, operators and predicate sets when we need to store them in the stack, in the plan or in the current state.

Some of those copies are not needed and we can just use the original object.

Sometimes, due to a cross dependence between two or more operators, the algorithm falls into an infinite loop.

When we detect one of those loops, we should stop the execution of the algorithm and throw an exception.

Currently, when we have to instantiate a partially instantiated predicate, we try to find a full instantiated predicate in our current state, and then we extract the constant values.

Problem: if the predicate is not in our current state, then the algorithm fails.

Proposal: if the predicate is not in our current state, then try to reach it using an operator.