“…On the other side, Finkel and Skrzypczak proved in [18] that there exist Σ 0 3 -complete, hence non Δ 0 3 , ω-languages accepted by non-deterministic onepartially-blind-counter Büchi automata. The existence of a Σ 1 1 -complete, hence non Borel, ω-language accepted by a Petri net was independently proved by Finkel and Skrzypczak in [17,34]. Moreover, Skrzypczak has proved in [34] that one blind counter is sufficient.…”