Left-definite variations of the classical Fourier expansion theorem. Littlejohn, L.L.; Zettl, A. — 2007 ETNA. Electronic Transactions on Numerical Analysis [electronic only]
An integral operator inequality with applications. Chisholm, R.S.; Everitt, W.N.; Littlejohn, L.L. — 1999 Journal of Inequalities and Applications [electronic only]