  Combining insights from the study of type refinement systems and of monoidal
closed chiralities, we show how to reconstruct Lawvere's hyperdoctrine of
presheaves using a full and faithful embedding into a monoidal closed
bifibration living now over the compact closed category of small categories and
distributors. Besides revealing dualities which are not immediately apparent in
the traditional presentation of the presheaf hyperdoctrine, this reconstruction
leads us to an axiomatic treatment of directed equality predicates (modelled by
hom presheaves), realizing a vision initially set out by Lawvere (1970). It
also leads to a simple calculus of string diagrams (representing presheaves)
that is highly reminiscent of C. S. Peirce's existential graphs for predicate
logic, refining an earlier interpretation of existential graphs in terms of
Boolean hyperdoctrines by Brady and Trimble. Finally, we illustrate how this
work extends to a bifibrational setting a number of fundamental ideas of linear
logic.
