Opaque OrdinalPool.getThreadR.

Lemma remLock_internal_step:
forall tp tp' m m' j (cntj: containsThread tp j) b ofs
(Hcomp: mem_compatible tp m)
(Hcomp': mem_compatible (remLockSet tp (b,ofs)) m)
(cntj': containsThread (remLockSet tp (b,ofs)) j)
(Hstep: internal_step cntj Hcomp tp' m'),
internal_step cntj' Hcomp' (remLockSet tp' (b,ofs)) m'.