anchor.diff:  (deftype multihash ()
     '(satisfies multihash-p))
   
  +;;; DECODE returns a DECODED-MULTIHASH
   (defstruct decoded-multihash
     "A multihash deconstructed into its parts."
     code name length digest)
  
positive.code: ;;; For more information, see: https://github.com/jbenet/multihash
  ;;; -- Copied from https://github.com/jbenet/multihash
  
  ;;; A multihash is a hash digest with 5 bytes of metadata prepended
  
  (in-package #:multihash)
  
  
negative.code:   ;;; length is the typical length of the digest
    (length nil :type fixnum :read-only t))
  
  ;;; replicating table here to:
  ;;; 1. avoid parsing the csv
  ;;; 2. ensuring errors in the csv don't screw up code.
  ;;; 3. changing a number has to happen in two places.
  (defparameter *definitions*
    ;;; name function-code length
    '((sha1 #x11 20)
  