func writeTransitions(ts system.TransitionSystem, labelNumberer *system.LabelNumberer, transitionsFilename string) {
serializer, ok := ts.(system.TransitionSerializer)
if !ok {
log.Fatal("Transition system does not implement transition serialization")
}
f, err := os.Create(transitionsFilename)
common.ExitIfError("Cannot create transition file:", err)
defer f.Close()
err = labelNumberer.WriteLabelNumberer(f, serializer)
common.ExitIfError("Cannot create label file:", err)
}
