Re: Defeasibility example

A. Background:
1. URIs (from http://tools.ietf.org/html/rfc3986)

 4.1 URI-reference = URI / relative-ref

 A URI-reference is either a URI or a relative reference.  If the
   URI-reference's prefix does not match the syntax of a scheme followed
   by its colon separator, then the URI-reference is a relative
   reference.