Lists in Prolog

“We like lists because we don’t want to die.”
—Umberto Eco

Prolog has a number of useful built-in relations for working with lists. These include:

Relation	Description
`append(X, Y, Z)`	True if appending lists X and Y yields Z
`reverse(X, Y)`	True if list X is the reverse of list Y
`permutation(X, Y)`	True if list X is a permutation of list Y
`sort(X, Y)`	True if list Y is the sort of list X
`length(L, N)`	True if list L has integer length N
`member(X, Y)`	True if X is an element of list Y

Example

Here are some examples of queries involving lists:

```
?- length([a,b,c,d], 4).`
```
Succeeds.
```
?- length([a,b,c], 4).
```
Fails.
```
?- length([a,b,c], N).
```
Succeeds with N = 3
```
?- length(L, 0).
```
Succeeds with L = []
```
?- member(c, [a,b,c,d]).
```
Succeeds.
```
?- member(e, [a,b,c,d]).
```
Fails.
```
?- member(X, [a,b,c,d]).
```
Can succeed in four ways,
namely X = a or X = b or X = c or X = d.
```
?- append([a], [b,c,d], L).
```
Succeeds with L = [a,b,c,d]
```
?- append(X, Y, [a,b,c,d]).
```
Can succeed in five ways, namely
X = [], Y = [a,b,c,d], or
X = [a], Y = [b,c,d], or …