A term in mathematical algebra, as well as graph theory
The following is an example of a lattice:
And another example:
A term in lattice theory
Consider the following lattice:
The leaf nodes are:
because they are lowermost in the lattice, right above the Absurdity element.
ContextA term in structure theory (Prolog).
A list is a structure which is a sequence of items, called elements.
For example, the following list has three elements:
A note on the word "structure" in the definition
Note that the word "structure" is used in this definition in a wider sense than in Prolog, where a structure is something quite specific. Here, the word "structure" is used in a broader sense, which also includes things like sets, graphs, sentence-diagrams, and everything else which has the essential properties of a structure.
A list is ordered
A list is ordered, which means that the order of the sequence matters.
For example, the following two lists are different lists:
They are different because, even though the elements are the same, their order is different.
A list may have duplicates
A list may contain the same element more than once. For example, the following list is a perfectly good list:<Mary,Mary>
The syntax does not matter
In the examples above, we have used the notation
It is important to realize that a list is an abstract entity which may have any syntactic realization in symbols. For example, these are all various syntactic representations of the same list:
The syntax is not important, except it must conform to whatever language we are expressing our lists in (e.g., Prolog+CG).