@article {GauGutLieNab13,
    AUTHOR = {Gaul, Andr{\'e} and Gutknecht, Martin H. and Liesen, J{\"o}rg 
              and Nabben, Reinhard},
     TITLE = {A framework for deflated and augmented {K}rylov subspace methods},
   JOURNAL = {SIAM J. Matrix Anal. Appl.},
  FJOURNAL = {SIAM Journal on Matrix Analysis and Applications},
    VOLUME = {31},
      YEAR = {2013},
    NUMBER = {2},
     PAGES = {495--518},
}