  This paper addresses the problem of merging uncertain information in the
framework of possibilistic logic. It presents several syntactic combination
rules to merge possibilistic knowledge bases, provided by different sources,
into a new possibilistic knowledge base. These combination rules are first
described at the meta-level outside the language of possibilistic logic. Next,
an extension of possibilistic logic, where the combination rules are inside the
language, is proposed. A proof system in a sequent form, which is sound and
complete with respect to the possibilistic logic semantics, is given.
