(*The blocks explicitly exported via call arguments, plus the already shared blocks*)
Definition exportedSrc mu vals b := orb (getBlocks vals b) (sharedSrc mu b).
Definition exportedTgt mu vals b := orb (getBlocks vals b) (sharedTgt mu b).

Lemma REACH_extern: forall mu (WD: SM_wd mu) m1 m2 vals1 vals2
(MemInjMu : Mem.inject (as_inj mu) m1 m2)
(ValInjMu : Forall2 (val_inject (as_inj mu)) vals1 vals2) b1
(R : REACH m1 (exportedSrc mu vals1) b1 = true)
(locBSrc : locBlocksSrc mu b1 = false),
exists b2 d, extern_of mu b1 = Some (b2, d).