Funny fact: 4 years ago I was looking for something what I would call today a "transitive similarity index" to measure similarity of shopping baskets of brick-and-mortar stores. Because I didn't find anything I "invented" my own algorithm. This year I implemented the same algorithm in a system which is live since yesterday. Googling up the Jaccard similarity I just realized that I re-invented a transitive version of it. Now my baby has a name. :)