TY  - JOUR
A1  - Dimitrova, Ilinka
A1  - Koppitz, Jörg
T1  - On relative ranks of the semigroup of orientation-preserving transformations on infinite chains
JF  - Asian-European journal of mathematics
N2  - In this paper, we determine the relative rank of the semigroup OP(X) of all orientation-preserving transformations on infinite chains modulo the semigroup O(X) of all order-preserving transformations.
KW  - Transformation semigroups on infinite chains
KW  - order-preserving
KW  - transformations
KW  - orientation-preserving transformations
KW  - relative rank
Y1  - 2020
U6  - https://doi.org/10.1142/S1793557121501461
SN  - 1793-5571
SN  - 1793-7183
VL  - 14
IS  - 08
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Dimitrova, Ilinka
A1  - Koppitz, Jörg
T1  - On relative ranks of the semigroup of orientation-preserving transformations on infinite chain with restricted range
JF  - Communications in algebra
N2  - Let X be an infinite linearly ordered set and let Y be a nonempty subset of X. We calculate the relative rank of the semigroup OP(X,Y) of all orientation-preserving transformations on X with restricted range Y modulo the semigroup O(X,Y) of all order-preserving transformations on X with restricted range Y. For Y = X, we characterize the relative generating sets of minimal size.
KW  - Order-preserving transformations
KW  - orientation-preserving
KW  - transformations
KW  - relative rank
KW  - restricted range
KW  - transformation
KW  - semigroups on infinite chain
Y1  - 2022
U6  - https://doi.org/10.1080/00927872.2021.2000998
SN  - 0092-7872
SN  - 1532-4125
VL  - 50
IS  - 5
SP  - 2157
EP  - 2168
PB  - Taylor & Francis Group
CY  - Philadelphia
ER  - 
TY  - JOUR
A1  - Dimitrova, Ilinka
A1  - Fernandes, Vitor H.
A1  - Koppitz, Jörg
T1  - A note on generators of the endomorphism semigroup of an infinite countable chain
JF  - Journal of Algebra and its Applications
N2  - In this note, we consider the semigroup O(X) of all order endomorphisms of an infinite chain X and the subset J of O(X) of all transformations alpha such that vertical bar Im(alpha)vertical bar = vertical bar X vertical bar. For an infinite countable chain X, we give a necessary and sufficient condition on X for O(X) = < J > to hold. We also present a sufficient condition on X for O(X) = < J > to hold, for an arbitrary infinite chain X.
KW  - Infinite chain
KW  - endomorphism semigroup
KW  - generators
KW  - relative rank
Y1  - 2016
U6  - https://doi.org/10.1142/S0219498817500311
SN  - 0219-4988
SN  - 1793-6829
VL  - 16
IS  - 2
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Dimitrova, Ilinka
A1  - Koppitz, Jörg
T1  - On the semigroup of all partial fence-preserving injections on a finite set
JF  - Journal of Algebra and Its Applications
N2  - For n∈N , let Xn={a1,a2,…,an} be an n-element set and let F=(Xn;<f) be a fence, also called a zigzag poset. As usual, we denote by In the symmetric inverse semigroup on Xn. We say that a transformation α∈In is fence-preserving if x<fy implies that xα<fyα, for all x,y in the domain of α. In this paper, we study the semigroup PFIn of all partial fence-preserving injections of Xn and its subsemigroup IFn={α∈PFIn:α−1∈PFIn}. Clearly, IFn is an inverse semigroup and contains all regular elements of PFIn. We characterize the Green’s relations for the semigroup IFn. Further, we prove that the semigroup IFn is generated by its elements with rank ≥n−2. Moreover, for n∈2N, we find the least generating set and calculate the rank of IFn.
KW  - Finite transformation semigroup
KW  - fence-preserving transformations
KW  - inverse semigroup
KW  - Green´s Relations
KW  - generators
KW  - rank
Y1  - 2017
U6  - https://doi.org/10.1142/S0219498817502231
SN  - 0219-4988
SN  - 1793-6829
VL  - 16
IS  - 12
PB  - World Scientific
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Fernandes, Vitor H.
A1  - Koppitz, Jörg
A1  - Musunthia, Tiwadee
T1  - The Rank of the Semigroup of All Order-Preserving Transformations on a Finite Fence
JF  - Bulletin of the Malaysian Mathematical Sciences Society volume
N2  - A zig-zag (or fence) order is a special partial order on a (finite) set. In this paper, we consider the semigroup TFn of all order-preserving transformations on an n-element zig-zag-ordered set. We determine the rank of TFn and provide a minimal generating set for TFn. Moreover, a formula for the number of idempotents in TFn is given.
KW  - Transformation semigroups
KW  - Rank of semigroup
KW  - Idempotents
KW  - Order-preserving
KW  - Fence
KW  - Zig-zag order
Y1  - 2019
U6  - https://doi.org/10.1007/s40840-017-0598-1
SN  - 0126-6705
SN  - 2180-4206
VL  - 42
IS  - 5
SP  - 2191
EP  - 2211
PB  - Malaysian mathematical sciences sciences soc
CY  - Pulau Punang
ER  - 
TY  - JOUR
A1  - Denecke, Klaus-Dieter
A1  - Koppitz, Jörg
A1  - Štrakov, Slavčo
T1  - Multi-hypersubstitutions and colored solid varieties
JF  - International journal of algebra and computation
N2  - Hypersubstitutions are mappings which map operation symbols to terms. Terms can be visualized by trees. Hypersubstitutions can be extended to mappings defined on sets of trees. The nodes of the trees, describing terms, are labelled by operation symbols and by colors, i.e. certain positive integers. We are interested in mappings which map differently-colored operation symbols to different terms. In this paper we extend the theory of hypersubstitutions and solid varieties to multi-hypersubstitutions and colored solid varieties. We develop the interconnections between such colored terms and multihypersubstitutions and the equational theory of Universal Algebra. The collection of all varieties of a given type forms a complete lattice which is very complex and difficult to study; multi-hypersubstitutions and colored solid varieties offer a new method to study complete sublattices of this lattice.
KW  - coloration of terms
KW  - multi-hypersubstitutions
KW  - colored solid varieties
Y1  - 2006
U6  - https://doi.org/10.1142/S0218196706003189
SN  - 0218-1967
VL  - 16
IS  - 4
SP  - 797
EP  - 815
PB  - World Scient. Publ.
CY  - Singapore
ER  - 
TY  - JOUR
A1  - Musunthia, Tiwadee
A1  - Koppitz, Jörg
T1  - Maximal subsemigroups of some semigroups of order-preserving mappings on a countably infinite set
JF  - Forum mathematicum
N2  - In this paper, we study the maximal subsemigroups of several semigroups of order-preserving transformations on the natural numbers and the integers, respectively. We determine all maximal subsemigroups of the monoid of all order-preserving injections on the set of natural numbers as well as on the set of integers. Further, we give all maximal subsemigroups of the monoid of all bijections on the integers. For the monoid of all order-preserving transformations on the natural numbers, we classify also all its maximal subsemigroups, containing a particular set of transformations.
KW  - Transformation semigroups
KW  - maximal subsemigroups
KW  - order-preserving mappings
Y1  - 2017
U6  - https://doi.org/10.1515/forum-2015-0093
SN  - 0933-7741
SN  - 1435-5337
VL  - 29
SP  - 971
EP  - 984
PB  - De Gruyter
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Tinpun, Kittisak
A1  - Koppitz, Jörg
T1  - Generating sets of infinite full transformation semigroups with restricted range
JF  - Acta scientiarum mathematicarum
N2  - In the present paper, we consider minimal generating sets of infinite full transformation semigroups with restricted range modulo specific subsets. In particular, we determine relative ranks.
KW  - generating sets
KW  - transformation semigroups
KW  - restricted range
KW  - relative ranks
Y1  - 2016
U6  - https://doi.org/10.14232/actasm-015-502-4
SN  - 0001-6969
VL  - 82
SP  - 55
EP  - 63
PB  - Institutum Bolyaianum Universitatis Szegediensis
CY  - Szeged
ER  - 
TY  - JOUR
A1  - Shtrakov, Slavcho
A1  - Koppitz, Jörg
T1  - Stable varieties of semigroups and groupoids
JF  - Algebra universalis
N2  - The paper deals with Sigma-composition and Sigma-essential composition of terms which lead to stable and s-stable varieties of algebras. A full description of all stable varieties of semigroups, commutative and idempotent groupoids is obtained. We use an abstract reduction system which simplifies the presentations of terms of type tau - (2) to study the variety of idempotent groupoids and s-stable varieties of groupoids. S-stable varieties are a variation of stable varieties, used to highlight replacement of subterms of a term in a deductive system instead of the usual replacement of variables by terms.
KW  - composition of terms
KW  - essential position in terms
KW  - stable variety
Y1  - 2016
U6  - https://doi.org/10.1007/s00012-015-0359-7
SN  - 0002-5240
SN  - 1420-8911
VL  - 75
SP  - 85
EP  - 106
PB  - Springer
CY  - Basel
ER  - 
TY  - JOUR
A1  - Koppitz, Jörg
T1  - Separation of O-n from its proper subsemigroups by a single identity
JF  - Semigroup forum
N2  - For each , we construct an identity that fails in the semigroup of all order-preserving maps on the -element chain but holds in each proper subsemigroup of O-n.
KW  - Order-preserving maps
KW  - Identities
Y1  - 2015
U6  - https://doi.org/10.1007/s00233-014-9674-0
SN  - 0037-1912
SN  - 1432-2137
VL  - 91
IS  - 1
SP  - 128
EP  - 138
PB  - Springer
CY  - New York
ER  -