@article {mcninch03:MR1992546,
    AUTHOR = {McNinch, George},
     TITLE = {Sub-principal homomorphisms in positive characteristic},
   JOURNAL = {Math. Z.},
  FJOURNAL = {Mathematische Zeitschrift},
    VOLUME = 244,
      YEAR = 2003,
    NUMBER = 2,
     PAGES = {433--455},
      OPTISSN = {0025-5874},
     CODEN = {MAZEAX},
   MRCLASS = {20G15 (17B45 20G40)},
  optMRNUMBER = 1992546,
MRREVIEWER = {James E. Humphreys},
}