The default citation styles verbose-trad1+; verbose-trad2 ;
verbose-trad3 use the op. cit. form in order to have shorter
reference when a title have been already cited. However, when
you cite two entries which share the same booktitle but not the
same title, the op. cit. mechanism does not work. This package
enables to obtain references like this: Author1, Title, in
Booktitle, Location, Publiser, Year, pages xxx Author2, Title2,
in Booktitle, op. cit, pages.
