Works citing   [Publ. RIMS 49 (2013), 831-859]

1. J. Behrndt, G. Grubb, M. Langer and V. Lotoreichik:
   Spectral asymptotics for resolvent differences of elliptic operators with delta and delta'-interactions on hypersurfaces,
   J. Spectr. Theory 5 (2015), 697-729.
   
   
2. B. T. Kaynak and O. T. Turgut:
   Infinitely many singular interactions on noncompact manifolds,
   Ann. Phys. 356 (2015), 426-437.