Research output: Contribution to journal › Article › peer-review
Extensions and covers for semigroups whose idempotents form a left regular band. / Branco, Mario J. J.; Gomes, Gracinda M. S.; Gould, Victoria.
In: Semigroup forum, Vol. 81, No. 1, 08.2010, p. 51-70.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Extensions and covers for semigroups whose idempotents form a left regular band
AU - Branco, Mario J. J.
AU - Gomes, Gracinda M. S.
AU - Gould, Victoria
PY - 2010/8
Y1 - 2010/8
N2 - Proper extensions that are "injective on a"'-related idempotents" of a">-unipotent semigroups, and much more generally of the class of generalised left restriction semigroups possessing the ample and congruence conditions, referred to here as glrac semigroups, are described as certain subalgebras of a lambda-semidirect product of a left regular band by an a">-unipotent or by a glrac semigroup, respectively. An example of such is the generalized Szendrei expansion.As a consequence of our embedding, we are able to give a structure theorem for proper left restriction semigroups. Further, we show that any glrac semigroup S has a proper cover that is a semidirect product of a left regular band by a monoid, and if S is left restriction, the left regular band may be taken to be a semilattice.
AB - Proper extensions that are "injective on a"'-related idempotents" of a">-unipotent semigroups, and much more generally of the class of generalised left restriction semigroups possessing the ample and congruence conditions, referred to here as glrac semigroups, are described as certain subalgebras of a lambda-semidirect product of a left regular band by an a">-unipotent or by a glrac semigroup, respectively. An example of such is the generalized Szendrei expansion.As a consequence of our embedding, we are able to give a structure theorem for proper left restriction semigroups. Further, we show that any glrac semigroup S has a proper cover that is a semidirect product of a left regular band by a monoid, and if S is left restriction, the left regular band may be taken to be a semilattice.
KW - Expansions
KW - R-unipotent semigroups
KW - Generalised restriction
KW - LEFT AMPLE SEMIGROUPS
KW - UNIPOTENT SEMIGROUP
KW - INVERSE-SEMIGROUPS
KW - EXPANSION
KW - MONOIDS
UR - http://www.scopus.com/inward/record.url?scp=77954860335&partnerID=8YFLogxK
U2 - 10.1007/s00233-010-9239-9
DO - 10.1007/s00233-010-9239-9
M3 - Article
VL - 81
SP - 51
EP - 70
JO - Semigroup forum
JF - Semigroup forum
SN - 0037-1912
IS - 1
ER -