Opaque OrdinalPool.getThreadR.

Lemma addThread_internal_execution:
forall tp tp' m m' i j xs vf arg pmap
(Hneq: i <> j)
(Hinv': invariant (addThread tp vf arg pmap))
(Hcomp': mem_compatible (addThread tp vf arg pmap) m)
(Hexec: internal_execution [seq x <- xs | x == j] tp m tp' m'),
internal_execution [seq x <- xs | x == j]
(addThread tp vf arg pmap) m
(addThread tp' vf arg pmap) m'.