Currently this just modifies the rule but not any of the proofs that use
it. The old version is kept for now but should be removed once all of
the proofs are updated.
Signed-off-by: Corey Lewis <Corey.Lewis@data61.csiro.au>
Isabelle2020 requires each session to declare it own set of directories that
may not overlap with other session's directories. This commit reorganises
files to comply with that requirement.
Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>