Performing Boolean Operations in GRASS 4.0.. - Van Warren.. (1991)(Correct)
a i r o t u T m a r g o r P e n i b m o c .r L. Van Warren t l e v r e t s e W s e m a J Scott Tweddale s
in GRASS 4.0: r.combine Program tutorial L. Van Warren, James Westervelt, Scott Tweddale www.geog.uni-hannover.de/grass/gdp/raster/combine.ps.gz