One recurring topic is the (open) knight's tour on the half board [52, 53]. There are cute proofs of the impossibility of a closed tour on 4 x n boards; Honsberger gives P6sa's proof [32, p. 145], and Gardner [22] gives a proof that he attributes to Golomb. The connection between knight tours on the 4 x 4 board (minus one square) and the
15 puzzle was investigated in this MAGAZINE in 1993 [34]. The number of knight's tours on the 8 x 8 board [46, 49] and the n x n board [43] have both been studied. Heuristics for generating tours are given by Shufelt and Berliner [67]. Boards of other shapes have also been studied [42; 47, Vol. 4]. Tours on the cylinder, Mobius band and Klein bottle appear in the "fanciful" account of Stewart [69, Chapter 7] and are studied in Watkins [78]. See Eggleton and Eid [17] for tours on infinite boards. For tours on boards with hexagonal tiles, see [44].