@article{MM2_1991__70_1_155585,
     author = {June M. Parker},
     title = {The sigma-core of a cooperative game.},
     journal = {Manuscripta mathematica},
     pages = {247--254},
     publisher = {mathdoc},
     volume = {70},
     number = {1},
     year = {1991},
     zbl = {0737.90081},
     url = {http://geodesic.mathdoc.fr/item/MM2_1991__70_1_155585/}
}