@article {MR1065343,
    AUTHOR = {Kawski, Matthias},
     TITLE = {The complexity of deciding controllability},
   JOURNAL = {Systems Control Lett.},
  FJOURNAL = {Systems \& Control Letters},
    VOLUME = {15},
      YEAR = {1990},
    NUMBER = {1},
     PAGES = {9--14},
      ISSN = {0167-6911},
     CODEN = {SCLEDC},
   MRCLASS = {93B05 (93B40)},
  MRNUMBER = {MR1065343 (91e:93009)},
}