Opaque containsThread.

(** FineConc is spinlock well-synchronized, strengthened version of the theorem*)
Theorem fineConc_spinlock_strong:
forall U U0 U' tr tr' tp m tp0 m0 tp' m'
(Hsynced: spinlock_synchronized tr)
(Hexec0: multi_fstep (U0, [::], tp0) m0 (U, tr, tp) m)
(Hexec: multi_fstep (U, tr, tp) m (U', tr ++ tr', tp') m'),
spinlock_synchronized (tr ++ tr').