anchor.diff:  (defpattern ps (pattern)
     (pattern
      pstream)
  -  :documentation "Defines a pattern whose pstream will be preserved to subsequent calls to `as-pstream'. To reset the pstream, simply re-evaluate the ps definition.
  +  :documentation "Preserve pstream state across subsequent calls to `as-pstream'. To reset the pstream, simply re-evaluate the ps definition.
   
   Based on the pattern originally from the miSCellaneous SuperCollider library.
   
   Example:
   
  -;; (defparameter pst (ps (pseries)))
  -;;
  -;; (next-upto-n pst 4)
  +;; (defparameter *pst* (ps (pseries)))
  +;;
  +;; (next-upto-n *pst* 4)
   ;; ;=> (0 1 2 3)
   ;;
  -;; (next-upto-n pst 4)
  +;; (next-upto-n *pst* 4)
   ;; ;=> (4 5 6 7)
   ;;
  -;; (defparameter pst (ps (pseries)))
  -;;
  -;; (next-upto-n pst 4)
  +;; (defparameter *pst* (ps (pseries)))
  +;;
  +;; (next-upto-n *pst* 4)
   ;; ;=> (0 1 2 3)
   
   See also: `pdef'"
  
positive.code:   (typep object 'pattern))
  
  (defun all-patterns ()
    "Get a list of all defined patterns.
  
  See also: `all-pdefs'"
    *patterns*)
  
negative.code: ;;; pattern glue
  
  (defun make-default-event ()
    "Get `*event*' if it's not nil, or get a fresh empty event."
    (or *event* (event)))
  
  (defun set-parents (pattern)
  