SWI-Prolog -- sort/2

Documentation
- Reference manual
  - Built-in Predicates
    - Built-in list operations
      - is_list/1
      - memberchk/2
      - length/2
      - sort/2
      - sort/4
      - msort/2
      - keysort/2
      - predsort/3
- Packages

Availability:built-in

[ISO]sort(+List, -Sorted)

True if Sorted can be unified with a list holding the elements of List, sorted to the standard order of terms (see section 4.7). Duplicates are removed. The implementation is in C, using natural merge sort.^{123Contributed
by Richard O'Keefe.} The sort/2 predicate can sort a cyclic list, returning a non-cyclic version with the same elements.

Note that List may contain non-ground terms. If Sorted is unbound at call-time, for each consequtive pair of elements in Sorted, the relation E1 @< E2 will hold. However, unifying a variable in Sorted may cause this relation to become invalid, even unifying a variable in Sorted with another (older) variable. See also section 4.7.1.