Prelude.ISNFunctions for manipulating ISBNs and ISSNs.
(norm str) normalizes an ISN, by removing all insignificant punctuation (spaces, hyphens, etc), leaving only the significant characters (digits, 'x', and 'X').
module ISBN : sig ... endInternational Standard Book Numbers (ISBNs)
module ISSN : sig ... endInternational Standard Serial Numbers (ISSNs)