@TechReport{Dartmouth:TR92-181,
  author = {Glenn Hurlbert and Garth Isaak},
  title = {{On The De Bruijn Torus Problem}},
  institution = {Dartmouth College, Computer Science},
  address = {Hanover, NH},
  number = {PCS-TR92-181},
  year = {1992},
  URL = {http://www.cs.dartmouth.edu/reports/TR92-181.pdf},
  abstract = {
    	A (kn;n)k-de Bruijn Cycle is a cyclic k-ary sequence with the
    property that every k-ary n-tuple appears exactly once contiguously on
    the cycle.  A (kr, ks; m, n)k-de Bruijn Torus is a k-ary krXks
    toroidal array with the property that every k-ary m x n matrix appears
    exactly once contiguously on the torus.  As is the case with de Bruijn
    cycles, the 2-dimensional version has many interesting applications,
    from coding and communications to pseudo-random arrays, spectral
    imaging, and robot self-location.  J.C. Cock proved the existence of
    such tori for all m, n, and k, and Chung, Diaconis, and Graham asked
    if it were possible that r = s and m -= n for n even.  Fan, Fan, Ma
    and Siu showed this was possible for k - 2.  Combining new techniques
    with old, we prove the result for k > 2 and show that actually much
    more is possible.  The cases in 3 or more dimensions remain.
  }
}