1. Ю. И. Хмелевский,Уравнения в своободной полугруппе, М., “Наука”, 1971.
2. L.A. Kaloujnine,Sur les p-groupes de Sylow du groupe symétrique du degré p, C. R. Acad. Sci., Paris, 221 (1945), 222–224.
3. R.P. Hunter,Some results on wreath products of semigroups, Bull. Soc., Math. Belgique, 18, 1966, 3–16.
4. B.H. Neumann,Embedding theorems for semigroups, J. London Math. Soc., 35, (1960), 184–192.
5. J.D. McKnight, Jr. and E. Sadowski,The kernel of the wreath product of semigroups, Semigroup Forum, 4, (1972), 232–236.