anchor.diff:  							   (cl-cairo2:stroke))))
   
   (defun to-cart (len angle)
  +  "Convert a length and angle (polar coordinates) into x,y rectangular coordinates."
     (values (* (cos (deg-to-rad angle)) len) (* (sin (deg-to-rad angle)) len)))
   
  -(defun fractal-tree (fname &key (length 600) (maxdepth 4) (limbs 2) (width 800) (height 600))
  +(defun fractal-tree (file-name &key (length 600) (maxdepth 4) (limbs 2) (width 800) (height 600))
  +  "Draw a fractal tree into the specified file, recursing to maxdepth, with the specified number of limbs at each level."
     (cl-cairo2:with-png-file
  -   ((home-dir fname) :argb32 width height)
  +   ((home-dir file-name) :argb32 width height)
   
      (cl-cairo2:set-source-rgba 0.0 0.0 0.0 1.0)
      (cl-cairo2:paint)
  
positive.code: 		   (if (and (< rxs width) (< rys height) (> rxs 0) (> rys 0))
  			   (set-pixel img (truncate rys) (truncate rxs) 255 255 255)))
  		  )))
  	  (with-open-file (output file :element-type '(unsigned-byte 8) :direction :output :if-exists :supersede)
  					(png:encode img output))))
  
  
  (defun strange-attractor (&key (file) (xxmin -2.0) (xxmax 2.0) (yymin -2.0) (yymax 2.0)
  							   (width 1600) (height 1600) (iter1 1000) (iter2 5000)
  							   (a 2.24)
  							   (b 0.43)
  							   (c -0.65)
  							   (d -2.43)
  							   (e 1.0))
    (let ((xinc (/ width (- xxmax xxmin)))
  		(yinc (/ height (- yymax yymin)))
  		(x 0)
  
negative.code: 		 ((unsigned-byte 32) (unsigned-byte 32) double-float double-float )) map-val))
  
  (defun set-pixel (img x y r g b)
    "Set a pixel in im at location x,y to color (r,g,b)"
    (setf (aref img x y 0) r)
    (setf (aref img x y 1) g)
    (setf (aref img x y 2) b))
  
  (defun increment-pixel (img x y)
    "Increment each color component of the pixel in img at location x,y by 1"
    (if (< (aref img y x 0) 255)
  	  (progn 
  		(incf (aref img y x 0))
  