Definition Jspec' := (@OK_spec (Concurrent_Espec unit CS ext_link)).

Theorem preservation ge Gamma n state state' : ~ blocked_at_external state CREATE -> ~ blocked_at_external state MKLOCK -> ~ blocked_at_external state FREE_LOCK -> ~ blocked_at_external state UNLOCK -> state_step state state' -> state_invariant Jspec' Gamma (S n) state -> state_bupd(ge := ge) (state_invariant Jspec' Gamma n) state' \/ state_bupd(ge := ge) (state_invariant Jspec' Gamma (S n)) state'.