(** Exploiting determinacy *)

Remark silent_or_not_silent:
  forall t, t = E0 \/ t <> E0.

Lemma f2b_determinacy_inv: forall s2 t' s2' t'' s2'', Step L2 s2 t' s2' -> Step L2 s2 t'' s2'' -> (t' = E0 /\ t'' = E0 /\ s2' = s2'') \/ (t' <> E0 /\ t'' <> E0 /\ match_traces (symbolenv L1) t' t'').