Guarded and Banded Semigroups |
| |
Authors: | Ernie Manes |
| |
Institution: | (1) Department of Mathematics and Statistics, University of Massachusetts, Amherst, MA 01003, USA |
| |
Abstract: | The variety of guarded semigroups consists of all (S,·, ˉ) where (S,·) is a semigroup and x ↦ \overline{x} is a unary operation
subject to four additional equations relating it to multiplication. The semigroup Pfn(X) of all partial transformations on
X is a guarded semigroup if x \overline{f} = x when xf is defined and is undefined otherwise. Every guarded semigroup is
a subalgebra of Pfn(X) for some X. A covering theorem of McAlister type is obtained. Free guarded semigroups are constructed
paralleling Scheiblich's construction of free inverse semigroups. The variety of banded semigroups has the same signature
but different equations. There is a canonical forgetful functor from guarded semigroups to banded semigroups. A semigroup
underlies a banded semigroup if and only if it is a split strong semilattice of right zero semigroups. Each banded semigroup
S contains a canonical subsemilattice g⋆(S). For any given semilattice L, a construction to synthesize the general banded semigroup S with g⋆ ≅ L is obtained. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|