“…Useful tools from algebraic topology and geometric topology for studying digital topological properties of a (binary) digital space include a digital covering space, the (digital) k-fundamental group, a digital k-surface, and so forth. These have been studied in papers including [1,2,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,25,26,31]. Recently, motivated by both a regular covering space and a Deck's transformation group in algebraic topology [32], their digital versions in digital covering theory have been developed [10,12,14,16], which play important roles in classifying digital covering spaces.…”