“…In recent years, many studies on ultradiscrete integrable systems, or integrable cellular automata have intensively been made by using various mathematical tools such as combinatorics [24,3,37,31], ultradiscretization procedure [35,27,34,14], crystal bases of quantum groups [9,7,8,11], and so forth. In particular, among many studies on geometric aspects of ultradiscrete integrable systems, several remarkable works have successively been made by Kimijima-Tokihiro [21], Inoue-Takenawa [12,13], and Iwao [17] in terms of tropical geometry and ultradiscretization procedure.…”