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struct FATransition : IComparable<FATransition> {
    public int Min; // -1 for Epsilon
    public int Max; // -1 for Epsilon
    public FA To;
    public FATransition(int min,int max,FA to) {
        Min = min;
        Max = max;
        To = to;
    }
    public FATransition(FA to) {
        Min = Max = -1;
        To = to;
    }
    public int CompareTo([AllowNull] FATransition other) {
        var c = Min.CompareTo(other.Min);
        if (c != 0) return c;
        return Max.CompareTo(other.Max);
    }
}
...
class FA {
...
    public bool IsDeterministic { get; private set; } = true;
    List<FATransition> _transitions = new List<FATransition>();
    public IList<FATransition> Transitions { get { return _transitions.AsReadOnly(); } }
...
}