If a bibliographic resource has more than one chief
source of information, choose the chief source
according to the following rules
(for example books in two or more volumes). If a resource
is in a number of separate parts, use the chief source
for the first part. If there is no first part, use the
chief source that gives the most information. If the
information differs in the chief sources of the other
parts, and if the difference is important, make a
note (see rule
7B5).