Proof using.
unfold locks_correct.
intros.
find_apply_hyp_hyp. break_exists.
eauto using at_head_of_queue_intro.
Qed.

(* Specifications: *)
Lemma at_head_of_nil :
forall sigma c,
at_head_of_queue sigma c ->
queue (sigma Server) = [] ->
False.
Lemma at_head_of_nil :
forall sigma c,
at_head_of_queue sigma c ->
queue (sigma Server) = [] ->
False.