The main difference with the strategy of Systre is that the categorisation of vertices bounds the number of candidates with respect to the maximal size of a category, hence the goal of having as many small categories as possible. However, the two strategies are exactly the same in the worst-case scenario where there is only one category. Note that, although rather complex, the constraints on the retained candidates described above can actually be implemented in an efficient way, which is necessary to prevent the search space reduction from taking more time than the actual search space exploration.