Within this framework, a square is classified as "terminal" if it has only one adjacent square, "medial" if it has two adjacent squares without any vertex of degree 2, and "kink" if it has two adjacent squares with a vertex of degree 2. A segment s is defined as a maximum linear chain along with a kink and/or terminal square. The count of squares within a segment is denoted by l(S) and indicates the length of the segment. By the way, a linear chain Li n comprises precisely one segment, while a zig-zag chain Z n consists of polyomino chains where all segments have lengths of 2 (see Figure ).