@article{SF_1971__2_133830,
     author = {K.K. Butler},
     title = {On {Kim's} conjecture.},
     journal = {Semigroup forum},
     pages = {281--281},
     publisher = {mathdoc},
     volume = {2},
     year = {1971},
     zbl = {0232.20125},
     url = {http://geodesic.mathdoc.fr/item/SF_1971__2_133830/}
}