@article{10_1017_S0017089500030767,
     author = {Petrich, Mario},
     title = {The kernel and trace operators for ideal extensions of regular semigroups},
     journal = {Glasgow mathematical journal},
     pages = {219--231},
     year = {1994},
     volume = {36},
     number = {2},
     doi = {10.1017/S0017089500030767},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500030767/}
}