REMARKS ON DIGITAL PRODUCTS WITH NORMAL ADJACENCY RELATIONS

To study product properties of digital spaces, we strongly need to formulate meaningful adjacency relations on digital prod- ucts. Thus the paper (7) rstly developed a normal adjacency re- lation on a digital product which can play an important role in studying the multiplicative property of a digital fundamental group, and product properties of digital coverings and digitally continuous maps. The present paper mainly surveys the normal adjacency re- lation on a digital product, improves the assertion of Boxer and Karaca in the paper (4) and restates Theorem 6.4 of the paper (19).