Pleijel, Åke Spectral theory for pairs of ordinary formally self-adjoint differential operators. (English) Zbl 0242.34027 J. Indian Math. Soc., n. Ser. 34(1970), 259-268 (1971). Page: −5 −4 −3 −2 −1 ±0 +1 +2 +3 +4 +5 Show Scanned Page Cited in 3 Documents MSC: 34B99 Boundary value problems for ordinary differential equations 47E05 General theory of ordinary differential operators (should also be assigned at least one other classification number in Section 47-XX) 34B20 Weyl theory and its generalizations for ordinary differential equations PDF BibTeX XML Cite \textit{Å. Pleijel}, J. Indian Math. Soc., New Ser. 34, 259--268 (1971; Zbl 0242.34027)