  We show that the theory of derivators (or, more generally, of fibered
multiderivators) on all small categories is equivalent to this theory on
partially ordered sets, in the following sense: Every derivator (more
generally, every fibered multiderivator) defined on partially ordered sets has
an enlargement to all small categories that is unique up to equivalence of
derivators. Furthermore, extending a theorem of Cisinski, we show that every
bifibration of multi-model categories (basically a collection of model
categories, and Quillen adjunctions in several variables between them) gives
rise to a left and right fibered multiderivator on all small categories.
