End COMPOSE_BACKWARD_SIMULATIONS.

(* Specifications: *)
Lemma compose_backward_simulation:
forall L1 L2 L3,
single_events L3 -> backward_simulation L1 L2 -> backward_simulation L2 L3 ->
backward_simulation L1 L3.
Lemma compose_backward_simulation:
forall L1 L2 L3,
single_events L3 -> backward_simulation L1 L2 -> backward_simulation L2 L3 ->
backward_simulation L1 L3.