tl;dr: multi-index Iterator for a structured finite tree (isomorphic to Cartesian product) with pre-defined skips.
IndexTree is an iterator that allows the traverse of a tree with a structure similar to the
Cartesian product of a finite amount of index-list, i.e. each level of the tree represents the
choice of a new index leaving the leaves to represent all the possible combinations of indices.
Motivation and a concrete application example can be found in this blog post.
This iterator is (extremely) useful for tackling this project.