Merge two items together, if it's possible. Returns null if it's not. E.g. 2 3 -> 6, x^2 x -> x^3, x y -> null @param item item which is already in

* Returns all ancestors of the element, with the oldest ancestor first and the element itself last. */

* Finds the common ancestor of the two elements, then returns whether an element of the given type exists between * the "current" node and that commo