run the given instructions, reverting to existing state upon
failure
Major Section: PROOF-CHECKER-COMMANDS
Example: (protect induct p prove) General Form: (protect &rest instruction-list)
Protect is the same as do-strict, except that as soon as an
instruction ``fails'', the state-stack reverts to what it was before
the protect instruction began, and restore is given the same meaning
that it had before the protect instruction began. See the
documentation for do-strict.
