= Sequences =
Sequence is a general notion of an ''Ordered'' one-dimensional structure. (Tables and Threes are usually 2-d structures, while graphs and molecules are 3-d structures).
The canonical example of a sequence is a {{{List}}} which is considered as a linear structure made out of pairs. {{{Pair}}} itself is an kind of an Ordered Sequence - it is a linear structure of exactly two elements with an explicit order. The [wiki:/AbstractDataTypes ADT] consists of {{{cons car cdr pair?}}}. Logically, Pair is a specialized instance of more general (and more abstract) type of Sequence, which implies ordered linear structure.