1. M. Abramowitz and I. A. Stegun,Handbook of Mathematical Functions, Dover, New York, 1972.
2. P. E. Appell,Sur la transformation des équations différentielles linéaires, Comptes Rendus91 (1880), 211–214.
3. W. Arendt,Gaussian estimates and interpolation of the spectrum in L p , Differential Integral Equations7 (1994), 1153–1168.
4. W. Arendt and A. F. M. ter Elst,Gaussian estimates for second order elliptic operators with boundary conditions, J. Operator Theory38 (1997), 87–130.
5. V. Batchenko and F. Gesztesy,The spectrum of Schrödinger operators with quasi-periodic algebrogeometric KdV potentials, Matematicheskaya Fizika, Analiz, Geometriya (Kharkov)10 (2003), 447–468.