An alternative to writing the domain of a sequence in the subscript is to indicate the range of values that the index can take by listing its highest and lowest legal values. For example, the notation formula_15 denotes the ten-term sequence of squares formula_16. The limits formula_17 and formula_18 are allowed, but they do not represent valid values for the index, only the supremum or infimum of such values, respectively. For example, the sequence formula_19 is the same as the sequence formula_8, and does not contain an additional term "at infinity". The sequence formula_21 is a bi-infinite sequence, and can also be written as formula_22.