A counterexample in Sturm–Liouville completeness theory

Paul Binding, Branko Ćurgus
2004 Proceedings of the Royal Society of Edinburgh. Section A Mathematics  
We give an example of an indefinite weight Sturm-Liouville problem whose eigenfunctions form a Riesz basis under Dirichlet boundary conditions but not under anti-periodic boundary conditions.
doi:10.1017/s030821050000319x fatcat:2xve4r6eu5dpxldjkmql2xrcvm