1. Nonlinear Spectral Theory;Appell,2004
2. Nonlinear spectral theory for homogeneous operators;Appell;Nonlinear Funct. Anal. Appl.,2002
3. Nonlinearity and Functional Analysis;Berger,1977
4. Half-eigenvalues of periodic Sturm–Liouville problems;Binding;J. Differential Equations,2004
5. Invariant points in function space;Birkhoff;Trans. Amer. Math. Soc.,1922