Description: Define the set of all closed walks of a fixed length n as words over
the set of vertices in a graph g . If 0 < n , such a word
corresponds to the sequence p(0) p(1) ... p(n-1) of the vertices in a
closed walk p(0) e(f(1)) p(1) e(f(2)) ... p(n-1) e(f(n)) p(n)=p(0) as
defined in df-clwlks . For n = 0 , the set is empty, see
clwwlkn0 . (Contributed by Alexander van der Vekens, 20-Mar-2018)(Revised by AV, 24-Apr-2021)(Revised by AV, 22-Mar-2022)