1. B. Arazi, An approach for generating different types of Gray codes, Information and Control 63(1984), 1–10.
2. F. M. Dekking, Strongly non-repetitive sequences and progression-free sets, J. Combinatorial Theory, 27(1979), 181–185.
3. T.C. Brown, Is there a sequence on four symbols in which no two adjacent segments are permutations of one another?, Amer. Math. Monthly 78(1971), 886–888.
4. L.J. Cummings, On the construction of Thue sequences, Proc. 9 th S-E Conf. on Combinatorics, Graph Theory, and Computing, pp. 235–242.
5. E.N. Gilbert, Gray codes and paths on the n-cube, Bell System Technical Journal 37(1958), 815–826.