  The Contextuality-by-Default theory is illustrated on contextuality analysis
of the idealized double-slit experiment. The experiment is described by a
system of contextually labeled binary random variables each of which answers
the question: has the particle hit the detector, having passed through a given
slit (left or right) in a given state (open or closed)? This system of random
variables is a cyclic system of rank 4, formally the same as the system
describing the EPR/Bell paradigm with signaling. Unlike the latter, however,
the system describing the double-slit experiment is always noncontextual, i.e.,
the context-dependence in it is entirely explainable in terms of direct
influences of contexts (closed-open arrangements of the slits) upon the
marginal distributions of the random variables involved. The analysis presented
is entirely within the framework of abstract classical probability theory (with
contextually labeled random variables). The only physical constraint used in
the analysis is that a particle cannot pass through a closed slit. The
noncontextuality of the double-slit system does not generalize to systems
describing experiments with more than two slits: in an abstract triple-slit
system, almost any set of observable detection probabilities is compatible with
both a contextual scenario and a noncontextual scenario of the particle passing
though various combinations of open and closed slits (although the issue of
physical realizability of these scenarios remains open).
