참고문헌
- American Math. Soc., Mathematical Surveys No. 7 The algebraic theory of semigroups A. H. Clifford;G. B. Preston
- Canadian J. Math. v.4 no.24 Restrictive semigroups of continuous functions on a 0-dimensional spaces R. Hofer
- Proc. London Math. Soc. v.5;2 no.3 Restrictive semigroups of continuous self-maps on arcwise connected spaces R. hofer
- Can. J. Math. v.20 Restrictive semigroups of closed functions K. D. Magill, Jr
- Proc. London Math. Soc. v.16 no.3 Semigroups of functions on topological spaces R. Hofer