predsort/3

Availability::- use_module(library(sort)).(can be autoloaded)

predsort(+Pred, +List, -Sorted)

Sorts similar to sort/2, but determines the order of two terms by calling Pred(-Delta, +E1, +E2) . This call must unify Delta with one of <, > or =. Duplicates are removed (i.e. equivalence classes of elements as defined by Pred are collapsed to a single element in Sorted) If the built-in predicate compare/3 is used, the result is the same as sort/2. See also keysort/2.