/// <summary>
 /// Construct instance from a normal-ordered sequence of ladder operators.
 /// </summary>
 /// <param name="ladderOperators">Normal-ordered sequence of ladder operators.</param>
 public NormalOrderedSequence(LadderSequence <TIndex> ladderOperators) : base(ladderOperators) => ThrowExceptionIfNotInNormalOrder();
 /// <summary>
 /// Constructs an instance from a normal-ordered sequence of ladder operators.
 /// </summary>
 /// <param name="ladderOperators">Normal-ordered sequence of ladder operators.</param>
 public IndexOrderedSequence(LadderSequence <TIndex> ladderOperators) : base(ladderOperators)
 {
     NormalizeToIndexOrder();
 }
 /// <summary>
 /// Constructor for an identitcal ladder operator sequence.
 /// </summary>
 public LadderSequence(LadderSequence <TIndex> setSequence)
 {
     Coefficient = setSequence.Coefficient;
     Sequence    = setSequence.Sequence.ToList();
 }