Almost symmetric numerical semigroups

@article{Herzog2019AlmostSN,
  title={Almost symmetric numerical semigroups},
  author={J{\"u}rgen Herzog and Kei-ichi Watanabe},
  journal={Semigroup Forum},
  year={2019},
  volume={98},
  pages={589-630}
}
We study almost symmetric numerical semigroups and semigroup rings. We describe a characteristic property of the minimal free resolution of the semigroup ring of an almost symmetric numerical semigroup. For almost symmetric semigroups generated by four elements we will give a structure theorem by using the “row-factorization matrices”, introduced by Moscariello. As a result, we give a simpler proof of Komeda’s structure theorem of pseudo-symmetric numerical semigroups generated by four elements… 
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