.. _library_derangements:

derangements

This library provides predicates for generating and querying derangements over lists. Derangements are full-length permutations where no result element is identical to the input element at the same position. The following categories of predicates are provided:

• Generation operations - Predicates for generating derangements.
• Ordering variants - Predicates that support an additional order argument (default, lexicographic, or shortlex) for controlling output order.
• Distinct-value generation - Predicates for generating derangements while deduplicating equal-valued results.
• Indexed access - Predicates for direct access to derangements at specific positions, including distinct derangements.
• Lexicographic stepping - Predicates for navigating derangements in lexicographic order.
• Counting operations - Predicates for counting derangements and distinct derangements.
• Random selection - Predicates for randomly selecting and sampling derangements and distinct derangements.

  Dedicated permutations, arrangements, cartesian_products, combinations, multisets, partitions, and subsequences libraries are also available for focused APIs on related operations.

API documentation

Open the `../../apis/library_index.html#derangements <../../apis/library_index.html#derangements>`__ link in a web browser.

Loading

To load all entities in this library, load the loader.lgt file:

::

| ?- logtalk_load(derangements(loader)).

Testing

To test this library predicates, load the tester.lgt file:

::

| ?- logtalk_load(derangements(tester)).