@article{ETNA_2007__27__a3,
     author = {Littlejohn, L.L. and Zettl, A.},
     title = {Left-definite variations of the classical {Fourier} expansion theorem},
     journal = {Electronic transactions on numerical analysis},
     pages = {124--139},
     publisher = {mathdoc},
     volume = {27},
     year = {2007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ETNA_2007__27__a3/}
}