@article{10_4153_CJM_1968_056_4,
     author = {Wallach, Nolan R.},
     title = {On {Maximal} {Subsystems} of {Root} {Systems}},
     journal = {Canadian journal of mathematics},
     pages = {555--574},
     year = {1968},
     volume = {20},
     number = {1},
     doi = {10.4153/CJM-1968-056-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1968-056-4/}
}