The length of the list S.
Return whether S is empty (has zero length).
Return the i-th term of the list S. If either i ≤0 or
i > #S + 1, then an error results.
Here i is allowed to be a multi-index (see Section Multi-indexing for
the interpretation).
Return the sublist of S given by the indices in the sequence I.
Each index in I must be in the range [1..l], where l is the length
of S.
Checks whether the ith item in L is defined or not, that is
it returns true if i is at most the length of L and false
otherwise.
V2.28, 13 July 2023