private static @NotNull Collection<SemKey<?>> getInheritorsSet(Map<SemKey<?>, Collection<SemKey<?>>> inheritors, SemKey<?> aSuper) {
    return inheritors.computeIfAbsent(aSuper, k -> new LinkedHashSet<>());
  }
private static @NotNull Collection<SemKey<?>> getInheritorsSet(Map<SemKey<?>, Collection<SemKey<?>>> inheritors, SemKey<?> aSuper)