@article{10_4153_CJM_1979_080_x,
     author = {Fong, C. K. and Sourour, A. R.},
     title = {On the {Operator} {Identity} \ensuremath{\sum} {AkXBk} \ensuremath{\equiv} 0},
     journal = {Canadian journal of mathematics},
     pages = {845--857},
     year = {1979},
     volume = {31},
     number = {4},
     doi = {10.4153/CJM-1979-080-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1979-080-x/}
}