# git-debrebase [<options>] launder-v0 # prints breakwater tip etc.
# git-debrebase [<options>] downstream-rebase-launder-v0 # experimental
#
-# git-debrebase [<options>] convert-from-gbp [<upstream-git-rev>]
# git-debrebase [<options>] convert-to-gbp
# problems / outstanding questions: