& btmapunits()2
 
  Error Messages:
 
  * If <MapOBJ> is not a valid map the function returns #-1 INVALID 
    MAP
  * If <x> falls outside the boundaries of the map the function 
    returns #-1 INVALID X COORD
  * If <y> falls outside the boundaries of the map the function 
    returns #-1 INVALID Y COORD
  * If <range> is < 0 the function returns #-1 INVALID RANGE
  * For other errors the function returns #-1 INVALID ARGUMENTS 
 
  Example:
  Given that #62 is a valid MapOBJ, with 2 units #1234 (at 10,10) and 
  #2345 (10,10,10) on it
 
  think btmapunits(#62) 
  #1234 #2345
  think btmapunits(#62,0,0,14)
  #1234 #2345
  think btmapunits(#62,0,0,0,14)
  #1234