@article{10.30755/NSJOM.2013.056,
     author = {QingShun Zhu},
     title = {Semilattices of nil-extensions of simple left
(right) $\pi$-regular ordered semigroups},
     journal = {Novi Sad Journal of Mathematics},
     pages = {27 - 34},
     publisher = {mathdoc},
     volume = {46},
     number = {1},
     year = {2016},
     doi = {10.30755/NSJOM.2013.056},
     url = {http://geodesic.mathdoc.fr/articles/10.30755/NSJOM.2013.056/}
}