Prokhorova, Marina Max Planck Institute for Mathematics, Max Planck Society;
https://doi.org/10.1007/s12220-019-00313-0 (Publisher version)
https://doi.org/10.48550/arXiv.1703.06105 (Preprint)
Prokhorova, M. (2021). Self-adjoint local boundary problems on compact surfaces. I. Spectral flow. The Journal of Geometric Analysis, 31(2), 1510-1554. doi:10.1007/s12220-019-00313-0.