actor-typed/src/main/scala/org/apache/pekko/actor/typed/internal/SystemMessage.scala
actor/src/main/scala/org/apache/pekko/dispatch/sysmsg/SystemMessage.scala

actor-typed/src/main/scala/org/apache/pekko/actor/typed/internal/ExtensionsImpl.scala
actor/src/main/scala/org/apache/pekko/actor/ActorSystem.scala

actor-typed/src/main/scala/org/apache/pekko/actor/typed/internal/Supervision.scala
actor/src/main/scala/org/apache/pekko/pattern/BackoffSupervisor.scala

actor-typed/src/main/scala/org/apache/pekko/actor/typed/internal/TimerSchedulerImpl.scala
actor/src/main/scala/org/apache/pekko/actor/dungeon/TimerSchedulerImpl.scala