@article{10_21136_CMJ_1977_101451,
     author = {Brown, Richard C. and Krall, Allan M.},
     title = {On minimizing the sum of squares of $\Cal L^2$ norms of differential operators under constraints},
     journal = {Czechoslovak Mathematical Journal},
     pages = {132--143},
     year = {1977},
     volume = {27},
     number = {1},
     doi = {10.21136/CMJ.1977.101451},
     mrnumber = {0430395},
     zbl = {0369.34007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1977.101451/}
}