The mechanism of fibring logics can be understood as a methodology which permits one to apply idiosyncratic properties of one given logic (propositional or modal, for instance) to other logics, creating hybrid systems for the sake of purely theoretical interests, or as suggested in several places in this book, directed to applications. The reader can appreciate the difficulties of a still elusive theory of fibring. Although with totally distinct backgrounds, the ideas of fibring, on the one hand, and splitting and splicing, on the other, seem to be complementary processes in the realm of logical systems whose relationships would contribute to the still to be determined general theory of combination of logics. This book is a good contribution in that direction. - Walter Carnielli, Mathematical Reviews, 2000