  We show that for any two von Neumann algebras $M$ and $N$, the space of
non-unital normal homomorphisms $N\to M$ with finite support, modulo
conjugation by unitaries in $M$, is Dedekind complete with respect to the
partial order coming from the addition of homomorphisms with orthogonal ranges;
this ties in with work by Brown and Capraro, where the corresponding objects
are given Banach space structures under various niceness conditions on $M$ and
$N$. More generally, we associate to $M$ a Grothendieck site-type category, and
show that presheaves satisfying a sheaf-like condition on this category give
rise to Dedekind complete lattices upon modding out unitary conjugation.
Examples include the above-mentioned spaces of morphisms, as well as analogous
spaces of completely positive or contractive maps. We also study conditions
under which these posets can be endowed with cone structures extending their
partial additions.
