@article {GreifSchotzau2007,
    AUTHOR = {Greif, Chen and Sch{\"o}tzau, Dominik},
     TITLE = {Preconditioners for the discretized time-harmonic {M}axwell
              equations in mixed form},
   JOURNAL = {Numer. Linear Algebra Appl.},
    VOLUME = {14},
      YEAR = {2007},
    NUMBER = {4},
     PAGES = {281--297}
}