“…Urn schemes, which were first studied by Pólya [48], are perhaps the simplest reinforcement models. They have many applications and generalizations [6]- [8], [11]- [13], [16], [17], [20], [21], [24], [25], [30]- [33], [35], [36], [39], [40], [45], [46], [48]. In general, reinforcement models typically adhere to the structure of 'rich get richer', which has also been termed positive reinforcement.…”