It is shown that for any quantum logic
L one can find a concrete logic
K and a surjective homomorphism
f from
K onto
L such that
f maps the centre of
K onto the centre of
L. Moreover, one can ensure that each finite set of compatible elements in
L is the image of a compatible subset of
K. This result is "best possible" - let a logic
L be the homomorphic image of a concrete logic under a homomorphism such that, if
F is a finite subset of the pre-image of a compatible subset of
L, then
F is compatible. Then
L must be concrete. In the second part one considers embeddings into concrete logics. It is shown that any concrete logic can be embedded into a concrete logic with preassigned centre and an abundance of two-valued measures. Finally, one proves that an arbitrary logic can be mapped into a concrete logic by a centrally additive mapping which preserves the ordering and complementation.
Let
L be a quantum logic and let
S(L) denote the set of all states on
L. (By a state we mean a nonnegative bounded
σ-additive measure, not necessarily normalized.) We ask whether every logic whose state space is a lattice has to be Boolean. We prove that this is so for finite logics and "projection logics." On the other hand, we show that there exist even concrete non-Boolean logics with a lattice state space (in fact, we prove that every countable concrete logic can be enlarged to a logic with a lattice state space). In the appendix we shortly consider the lattice properties of the set of observables and correct the paper [10].