@article {MandelMoitierVerfuerth2022,
    AUTHOR = {Mandel, Rainer and Moitier, Zo\"{i}s and Verf\"{u}rth, Barbara},
     TITLE = {Nonlinear {H}elmholtz equations with sign-changing diffusion
              coefficient},
   JOURNAL = {C. R. Math. Acad. Sci. Paris},
  FJOURNAL = {Comptes Rendus Math\'{e}matique. Acad\'{e}mie des Sciences. Paris},
    VOLUME = {360},
      YEAR = {2022},
     PAGES = {513--538},
      ISSN = {1631-073X},
   MRCLASS = {35B32 (47A10)},
       DOI = {10.5802/crmath.322},
       URL = {https://doi.org/10.5802/crmath.322},
}