@article{etna_vol27_pp124-139,
  author  = {L. L. Littlejohn and A. Zettl},
  title   = {Left-definite variations of the classical Fourier expansion theorem},
  journal = {Electron. Trans. Numer. Anal.},
  volume  = {27},
  year    = {2007},
  pages   = {124--139},
}