“…For previous results related to HNC the reader is referred to Burns [1], Imrich [8], Servatius [19], Stallings [21], Gersten [7], Nickolas [18], Walter Neumann [17], Feuerman [5], Tardos [22], Dicks [2], Dicks-Formanek [3], Khan [11], Meakin-Weil [13], Sergei Ivanov [9], [10], and Dicks-Ivanov [4]. A proof of SHNC has also been announced in a recent preprint by Joel Friedman [6].…”