LAST_ASSUMTactical.LAST_ASSUM : (thm_tactic -> tactic)
Maps a theorem-tactic over the assumptions, in reverse order, applying first successful tactic.
LAST_ASSUM behaves like FIRST_ASSUM, except
that it goes through the list of assumptions in reverse order
Tactical.FIRST_ASSUM,
Tactical.LAST_X_ASSUM