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@article{PIM_1977_N_S_22_36_a33, author = {Lee Sin-Min}, title = {Permutation {Group} {Extension} {Of} {Groupoids}}, journal = {Publications de l'Institut Math\'ematique}, pages = {255 }, publisher = {mathdoc}, volume = {_N_S_22}, number = {36}, year = {1977}, url = {http://geodesic.mathdoc.fr/item/PIM_1977_N_S_22_36_a33/} }
Lee Sin-Min. Permutation Group Extension Of Groupoids. Publications de l'Institut Mathématique, _N_S_22 (1977) no. 36, p. 255 . http://geodesic.mathdoc.fr/item/PIM_1977_N_S_22_36_a33/