@article {MR3246802,
    AUTHOR = {Carstensen, Carsten and Gedicke, Joscha},
     TITLE = {Guaranteed lower bounds for eigenvalues},
   JOURNAL = {Math. Comp.},
  FJOURNAL = {Mathematics of Computation},
    VOLUME = {83},
      YEAR = {2014},
    NUMBER = {290},
     PAGES = {2605--2629},
      ISSN = {0025-5718},
   MRCLASS = {65N25 (15A42 65N15 65N30 65N50)},
  MRNUMBER = {3246802},
MRREVIEWER = {J\'{a}n Lov\'{\i}\v{s}ek},
       DOI = {10.1090/S0025-5718-2014-02833-0},
       URL = {https://doi.org/10.1090/S0025-5718-2014-02833-0},
}