essentially it generates a graph out of all of your follows, and their follows follows, and their follows follows
it walks the graph and computes a weight for each, which technically could be a kind hamming distance, combined with a graph weighting
so to compute each WoT score it must repeatedly walk through each of your follows, check their follows, and search for a given candidate to evaluate
it's not as complicated as it sounds, but it is as complicated as it sounds
it's highly effective and honestly personally apart from irritating problems i have lately due to refusing to use free relays coracle's automated filtering is amazing