anchor.diff:  tree?,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-tree.htm#tree?
   
   ; c211 turtle library
  +turtle,library,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-turtle.htm
   hatch,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-turtle.htm#hatch
   clone,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-turtle.htm#clone
   live-display,parameter,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-turtle.htm#live-display
  
positive.code: ; c211 image library
  black,procedure,2,
  blue,procedure,2,
  color,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-image.htm#color
  
negative.code: matrix->vov,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-matrix.htm#matrix->vov
  vov->matrix,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-matrix.htm#vov->matrix
  
  ; c211 tree librar
  ; matrix,library,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-matrix.htm ; already a procedure
  draw-tree,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-tree.htm#draw-tree
  empty-tree,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-tree.htm#empty-tree
  empty-tree?,procedure,2,http://www.cs.indiana.edu/cgi-pub/c211/wombat/docs/c211-tree.htm#empty-tree?
  