@article {DesLie05,
    AUTHOR = {de Sturler, Eric and Liesen, J{\"o}rg},
     TITLE = {Block-diagonal and constraint preconditioners for 
              nonsymmetric indefinite linear systems. 
              {P}art {I}: {T}heory},
   JOURNAL = {SIAM J. Sci. Comput.},
  FJOURNAL = {SIAM Journal on Scientific Computing},
    VOLUME = {26},
      YEAR = {2005},
    NUMBER = {5},
     PAGES = {1598--1619},
}