György Pollák
Acta Sci. Math. (Szeged) 68:1-2(2002), 107-115 2831/2009
Abstract. We consider several natural quasi-orderings on free semigroups and describe minimal elements with respect to these quasi-orderings in some important sets of words.
AMS Subject Classification (1991): 20M05
(Registered under 2831/2009.)