REFERENCES
- Birget , J. C. ( 1984 ). Iteration of expansions—unambiguous semigroups . J. Pure Appl. Algebra 34 : 1 – 55 .
- Birget , J. C. ( 1984 ). Arbitrary vs. regular semigroups . J. Pure Appl. Algebra 34 : 57 – 115 .
- Clifford , A. H. , Preston , G. B. ( 1967 ). The Algebraic Theory of Semigroups I . Amer. Math. Soc. Providence, RI .
- McAlister , D. B. ( 1968 ). A homomorphism theorem for semigroups . J. London Math. Soc. 43 : 355 – 366 .
- Pin , J. E. ( 1986 ). Varieties of Formal Languages . London : North Oxford Academic Publishers Ltd .
- Trotter , P. G. ( 1980 ). Non existence of coreflections and coproducts in some subcategories of semigroups . Proc. Amer. Math. Soc. 80 : 10 – 14 .
- Communicated by V. Gould.