private static List<SpecificFilter> GetSpecificFilters(Dictionary<CrontabFieldKind, List<ICronFilter>> filters, CrontabFieldKind kind)
{
return filters[kind].Where(x => x.GetType() == typeof(SpecificFilter)).Cast<SpecificFilter>().Union(
filters[kind].Where(x => x.GetType() == typeof(RangeFilter)).SelectMany(x => ((RangeFilter)x).SpecificFilters)
).Union(
filters[kind].Where(x => x.GetType() == typeof(StepFilter)).SelectMany(x => ((StepFilter)x).SpecificFilters)
).ToList();
}