A reference to a personal communication between the author of the paper in which the bibliography appears and some other person. The ref.author of the reference is the person with whom the conversation was held.
(=> (= (Ref.Day ?Ref) ?Day) (Or (Article-Reference ?Ref) (Personal-Communication-Reference ?Ref))) (Subclass-Partition Non-Publication-Reference (Setof Personal-Communication-Reference Generic-Unpublished-Reference))