15.64.50.1  Options  - 

     1.  ALL - Turns on or off all shadowing options.
     2.  SYMBOL - Shadows the symbol.

     3.  X - Draws lines from point to back plane along the X axis. 
     4.  Y - Draws lines from point to back plane along the Y axis.
     5.  Z - Draws lines from point to back plane along the Z axis.
     6.  :XY - Shadows in XY plane.
     7.  YZ - Shadows in YZ plane when THREE=ON.
     8.  ZX - Shadows in ZX plane when THREE=ON.
     9.  INTENSITY  -  Sets  line  intensity  or  width (0-5).  0 gets the
         intensity from the SET INTENSITY or SET AXES command.
    10.  WHITE...  - Sets the line color.  (Default:Same as axes)
    11.  SOLID...   -  Sets  the  line  texture.   (Default:Same  as axes)
         See:Command SET TEXTURE.
    12.  SYMBOL  -  Draws  a symbol [sym] to be plotted at intersection of
         vertical and horizontal lines.  (Default:sym=0O)
    13.  PERMANENT  -  Sets the current shadow options permanently for all
         NEW plots.
If  no  options are specified, then all shadow parameters are reset to the
original defaults.
(Default:ALL=OFF)