Relative Category Theory and Geometric Morphisms

'The present book represents what must surely be an extreme point in the spectrum of possible approaches: the one which makes the greatest possible use of formal languages. The material, throughtout the books, is of a highly technical nature ... By providing a language adequate to handle indexed categories over a topos (and much more besides), the authors have done much to "demystify" indexed category theory and make it accessible to those for whom the sight of a 2-categorical diagram is liable to induce instant incomprehension. All such people ... should make the effort to master the technicalities in this book, if they wish to get closer to an understanding of what really goes on in the 2-category of toposes.'P.T. Johnstone, Zentralblatter, 1993

• Introduction; Local set theories; Partial function theory `L'; Equationals; Categories in a topos; Topoi in a topos; A representation theorem for geometric morphisms; Local set theories in S; The theory of a topos in S; Topologies and sheaves; The relative Giraud theorem; Appendices.