// output of ./demo/comb/debruijn-demo.cc:
// Description:
//% Generating De Bruijn sequences.

arg 1: 3 == m  [m-ary De Bruijn sequence]  default=3
arg 2: 4 == n  [length = m**n]  default=4

 n = 4  length = 81:
 0 0001 0002 0011 0012 0021 0022 01 0102 0111 0112 0121 0122 02 0211 0212 0221 0222 1 1112 1122 12 1222 2
000010002001100120021002201010201110112012101220202110212022102221111211221212222
 ct=81
