End FACTOR_FORWARD_SIMULATION.

(* Specifications: *)
Theorem factor_forward_simulation:
forall L1 L2,
forward_simulation L1 L2 -> single_events L2 ->
forward_simulation (atomic L1) L2.
Theorem factor_forward_simulation:
forall L1 L2,
forward_simulation L1 L2 -> single_events L2 ->
forward_simulation (atomic L1) L2.