See splitter for a discussion of splitter rules. See set-splitter-output for how to turn off, or on, the reporting of splitter
rules. When splitter-output is off, because either prove output is
inhibited
(see set-inhibit-output-lst) or (set-splitter-output
nil) has been invoked, then the value of (splitter-output) is nil.
Otherwise, such reporting is on and the value is non-nil.
