REFERENCES
- Clifford , A. H. , Preston , G. B. ( 1961 ). The Algebraic Theory of Semigroups I, Mathematical Surveys, N. 7 . Providence , R.I : American Mathematical Society .
- Fountain , J. ( 1979 ). Adequate semigroups . Proc. Edinburgh Math. Soc. (2) 22 ( 2 ): 113 – 125 .
- Fountain , J. ( 1982 ). Abundant semigroups . Proc. London Math. Soc. (3) 44 ( 1 ): 103 – 129 .
- Kambites , M. http://www.maths.manchester.ac.uk/mkambites/events/nbsan/
- Kambites , M. Free adequate semigroups . J. Aust. Math. Soc. to appear, arXiv:0902.0297 .
- McCune , W. ( 2009 ). Prover9 and Mace4. version 2009-11A. http://www.cs.unm.edu/ ∼mccune/prover9/
- Araújo , J. , Kinyon , M. , Malheiro , A. A characterization of adequate semigroups by forbidden subsemigroups. To appear in the Proceedings of the Royal Society of Edinburgh.
- Laradji , A. , Umar , A. ( 2004 ). On certain finite semigroups of order-decreasing transformations I . Semigroup Forum 69 : 184 – 200 .
- Communicated by V. Gould.