62 set_tree234
%--------------------------------------------------%
% vim: ts=4 sw=4 et ft=mercury
%--------------------------------------------------%
% Copyright (C) 2005-2006, 2009-2012 The University of Melbourne.
% This file may only be copied under the terms of the GNU Library General
% Public License - see the file COPYING.LIB in the Mercury distribution.
%--------------------------------------------------%
%
% File: set_tree234.m.
% Author: zs.
% Stability: high.
%
% This module implements sets using 2-3-4 trees.
%
%--------------------------------------------------%
%--------------------------------------------------%
:- module set_tree234.
:- interface.
:- import_module bool.
:- import_module list.
:- import_module set.
%--------------------------------------------------%
:- type set_tree234(_T).
% `set_tree234.init = Set' is true iff `Set' is an empty set.
%
:- func set_tree234.init = set_tree234(T).
% `set_tree234.singleton_set(Elem, Set)' is true iff `Set' is the set
% containing just the single element `Elem'.
%
:- pred set_tree234.singleton_set(T, set_tree234(T)).
:- mode set_tree234.singleton_set(in, out) is det.
:- mode set_tree234.singleton_set(out, in) is semidet.
:- func set_tree234.make_singleton_set(T) = set_tree234(T).
:- pred set_tree234.is_singleton(set_tree234(T)::in, T::out) is semidet.
% `set_tree234.empty(Set)' is true iff `Set' is an empty set.
%
:- pred set_tree234.empty(set_tree234(_T)::in) is semidet.
% A synonym for the above.
%
:- pred set_tree234.is_empty(set_tree234(_T)::in) is semidet.
:- pred set_tree234.non_empty(set_tree234(T)::in) is semidet.
:- pred set_tree234.is_non_empty(set_tree234(T)::in) is semidet.
% `set_tree234.member(X, Set)' is true iff `X' is a member of `Set'.
%
:- pred set_tree234.member(T, set_tree234(T)).
:- mode set_tree234.member(in, in) is semidet.
:- mode set_tree234.member(out, in) is nondet.
% `set_tree234.is_member(Set, X, Result)' returns
% `Result = yes' iff `X' is a member of `Set'.
%
:- func set_tree234.is_member(set_tree234(T), T) = bool.
:- pred set_tree234.is_member(set_tree234(T)::in, T::in, bool::out) is det.
% `set_tree234.contains(Set, X)' is true iff `X' is a member of `Set'.
%
:- pred set_tree234.contains(set_tree234(T)::in, T::in) is semidet.
% `set_tree234.list_to_set(List) = Set' is true iff `Set' is the set
% containing only the members of `List'.
%
:- func set_tree234.list_to_set(list(T)) = set_tree234(T).
:- pred set_tree234.list_to_set(list(T)::in, set_tree234(T)::out) is det.
:- func set_tree234.from_list(list(T)) = set_tree234(T).
:- pred set_tree234.from_list(list(T)::in, set_tree234(T)::out) is det.
% `set_tree234.sorted_list_to_set(List) = Set' is true iff `Set' is
% the set containing only the members of `List'. `List' must be sorted.
%
:- func set_tree234.sorted_list_to_set(list(T)) = set_tree234(T).
:- pred set_tree234.sorted_list_to_set(list(T)::in, set_tree234(T)::out) is det.
% `from_set(Set)' returns a set_tree234 containing only the members of
% `Set'. Takes O(card(Set)) time and space.
%
:- func from_set(set.set(T)) = set_tree234(T).
% `set_tree234.to_sorted_list(Set) = List' is true iff `List' is the
% list of all the members of `Set', in sorted order.
%
:- func set_tree234.to_sorted_list(set_tree234(T)) = list(T).
:- pred set_tree234.to_sorted_list(set_tree234(T)::in, list(T)::out) is det.
% `to_sorted_list(Set)' returns a set.set containing all the members
% of `Set', in sorted order. Takes O(card(Set)) time and space.
%
:- func to_set(set_tree234(T)) = set.set(T).
% `set_tree234.equal(SetA, SetB)' is true iff
% `SetA' and `SetB' contain the same elements.
%
:- pred set_tree234.equal(set_tree234(T)::in, set_tree234(T)::in) is semidet.
% `set_tree234.subset(SetA, SetB)' is true iff `SetA' is a subset of
% `SetB'.
%
:- pred set_tree234.subset(set_tree234(T)::in, set_tree234(T)::in) is semidet.
% `set_tree234.superset(SetA, SetB)' is true iff `SetA' is a
% superset of `SetB'.
%
:- pred set_tree234.superset(set_tree234(T)::in, set_tree234(T)::in)
is semidet.
% `set_tree234.insert(X, Set0, Set)' is true iff `Set' is the union
% of `Set0' and the set containing only `X'.
%
:- func set_tree234.insert(T, set_tree234(T)) = set_tree234(T).
:- pred set_tree234.insert(T::in, set_tree234(T)::in, set_tree234(T)::out)
is det.
% `set_tree234.insert_new(X, Set0, Set)' is true iff
% `Set0' does not contain `X', while `Set' is the union of `Set0'
% and the set containing only `X'.
%
:- pred set_tree234.insert_new(T::in,
set_tree234(T)::in, set_tree234(T)::out) is semidet.
% `set_tree234.insert_list(Xs, Set0, Set)' is true iff `Set' is the
% union of `Set0' and the set containing only the members of `Xs'.
%
:- func set_tree234.insert_list(list(T), set_tree234(T)) = set_tree234(T).
:- pred set_tree234.insert_list(list(T)::in,
set_tree234(T)::in, set_tree234(T)::out) is det.
% `set_tree234.delete(X, Set0, Set)' is true iff `Set' is the
% relative complement of `Set0' and the set containing only `X', i.e.
% if `Set' is the set which contains all the elements of `Set0'
% except `X'.
%
:- func set_tree234.delete(T, set_tree234(T)) = set_tree234(T).
:- pred set_tree234.delete(T::in, set_tree234(T)::in, set_tree234(T)::out)
is det.
% `set_tree234.delete_list(Xs, Set0, Set)' is true iff `Set' is the
% relative complement of `Set0' and the set containing only the members
% of `Xs'.
%
:- func set_tree234.delete_list(list(T), set_tree234(T)) = set_tree234(T).
:- pred set_tree234.delete_list(list(T)::in,
set_tree234(T)::in, set_tree234(T)::out) is det.
% `set_tree234.remove(X, Set0, Set)' is true iff `Set0' contains `X',
% and `Set' is the relative complement of `Set0' and the set
% containing only `X', i.e. if `Set' is the set which contains
% all the elements of `Set0' except `X'.
%
:- pred set_tree234.remove(T::in, set_tree234(T)::in, set_tree234(T)::out)
is semidet.
% `set_tree234.remove_list(Xs, Set0, Set)' is true iff Xs does not
% contain any duplicates, `Set0' contains every member of `Xs',
% and `Set' is the relative complement of `Set0' and the set
% containing only the members of `Xs'.
%
:- pred set_tree234.remove_list(list(T)::in,
set_tree234(T)::in, set_tree234(T)::out) is semidet.
% `set_tree234.remove_least(X, Set0, Set)' is true iff `X' is the
% least element in `Set0', and `Set' is the set which contains all the
% elements of `Set0' except `X'.
%
:- pred set_tree234.remove_least(T::out,
set_tree234(T)::in, set_tree234(T)::out) is semidet.
% `set_tree234.union(SetA, SetB) = Set' is true iff `Set' is the union
% of `SetA' and `SetB'.
%
:- func set_tree234.union(set_tree234(T), set_tree234(T)) = set_tree234(T).
:- pred set_tree234.union(set_tree234(T)::in, set_tree234(T)::in,
set_tree234(T)::out) is det.
% `set_tree234.union_list(A, B)' is true iff `B' is the union of
% all the sets in `A'
%
:- func set_tree234.union_list(list(set_tree234(T))) = set_tree234(T).
:- pred set_tree234.union_list(list(set_tree234(T))::in, set_tree234(T)::out)
is det.
% `set_tree234.power_union(A) = B' is true iff `B' is the union of
% all the sets in `A'
%
:- func set_tree234.power_union(set_tree234(set_tree234(T))) = set_tree234(T).
:- pred set_tree234.power_union(set_tree234(set_tree234(T))::in,
set_tree234(T)::out) is det.
% `set_tree234.intersect(SetA, SetB) = Set' is true iff `Set' is the
% intersection of `SetA' and `SetB'.
%
:- func set_tree234.intersect(set_tree234(T), set_tree234(T)) = set_tree234(T).
:- pred set_tree234.intersect(set_tree234(T)::in, set_tree234(T)::in,
set_tree234(T)::out) is det.
% `set_tree234.power_intersect(A, B)' is true iff `B' is the
% intersection of all the sets in `A'.
%
:- func set_tree234.power_intersect(set_tree234(set_tree234(T)))
= set_tree234(T).
:- pred set_tree234.power_intersect(set_tree234(set_tree234(T))::in,
set_tree234(T)::out) is det.
% `set_tree234.intersect_list(A, B)' is true iff `B' is the
% intersection of all the sets in `A'.
%
:- func set_tree234.intersect_list(list(set_tree234(T))) = set_tree234(T).
:- pred set_tree234.intersect_list(list(set_tree234(T))::in,
set_tree234(T)::out) is det.
% `set_tree234.difference(SetA, SetB, Set)' is true iff `Set' is the
% set containing all the elements of `SetA' except those that
% occur in `SetB'.
%
:- func set_tree234.difference(set_tree234(T), set_tree234(T))
= set_tree234(T).
:- pred set_tree234.difference(set_tree234(T)::in, set_tree234(T)::in,
set_tree234(T)::out) is det.
% `set_tree234.count(Set, Count)' is true iff `Set' has
% `Count' elements.
%
:- func set_tree234.count(set_tree234(T)) = int.
:- func set_tree234.map(func(T1) = T2, set_tree234(T1)) = set_tree234(T2).
:- pred set_tree234.map(pred(T1, T2)::in(pred(in, out) is det),
set_tree234(T1)::in, set_tree234(T2)::out) is det.
:- pred set_tree234.filter_map(pred(T1, T2)::in(pred(in, out) is semidet),
set_tree234(T1)::in, set_tree234(T2)::out) is det.
:- func set_tree234.filter_map(func(T1) = T2, set_tree234(T1))
= set_tree234(T2).
:- mode set_tree234.filter_map(func(in) = out is semidet, in) = out is det.
:- func set_tree234.fold(func(T1, T2) = T2, set_tree234(T1), T2) = T2.
:- pred set_tree234.fold(pred(T1, T2, T2), set_tree234(T1), T2, T2).
:- mode set_tree234.fold(pred(in, in, out) is det, in, in, out) is det.
:- mode set_tree234.fold(pred(in, mdi, muo) is det, in, mdi, muo) is det.
:- mode set_tree234.fold(pred(in, di, uo) is det, in, di, uo) is det.
:- mode set_tree234.fold(pred(in, in, out) is semidet, in, in, out)
is semidet.
:- mode set_tree234.fold(pred(in, mdi, muo) is semidet, in, mdi, muo)
is semidet.
:- mode set_tree234.fold(pred(in, di, uo) is semidet, in, di, uo)
is semidet.
:- func set_tree234.foldl(func(T1, T2) = T2, set_tree234(T1), T2) = T2.
:- pred set_tree234.foldl(pred(T1, T2, T2), set_tree234(T1), T2, T2).
:- mode set_tree234.foldl(pred(in, in, out) is det, in, in, out) is det.
:- mode set_tree234.foldl(pred(in, mdi, muo) is det, in, mdi, muo) is det.
:- mode set_tree234.foldl(pred(in, di, uo) is det, in, di, uo) is det.
:- mode set_tree234.foldl(pred(in, in, out) is semidet, in, in, out)
is semidet.
:- mode set_tree234.foldl(pred(in, mdi, muo) is semidet, in, mdi, muo)
is semidet.
:- mode set_tree234.foldl(pred(in, di, uo) is semidet, in, di, uo)
is semidet.
:- pred set_tree234.fold2(pred(T1, T2, T2, T3, T3), set_tree234(T1),
T2, T2, T3, T3).
:- mode set_tree234.fold2(pred(in, in, out, in, out) is det, in,
in, out, in, out) is det.
:- mode set_tree234.fold2(pred(in, in, out, mdi, muo) is det, in,
in, out, mdi, muo) is det.
:- mode set_tree234.fold2(pred(in, in, out, di, uo) is det, in,
in, out, di, uo) is det.
:- mode set_tree234.fold2(pred(in, in, out, in, out) is semidet, in,
in, out, in, out) is semidet.
:- mode set_tree234.fold2(pred(in, in, out, mdi, muo) is semidet, in,
in, out, mdi, muo) is semidet.
:- mode set_tree234.fold2(pred(in, in, out, di, uo) is semidet, in,
in, out, di, uo) is semidet.
:- pred set_tree234.foldl2(pred(T1, T2, T2, T3, T3), set_tree234(T1),
T2, T2, T3, T3).
:- mode set_tree234.foldl2(pred(in, in, out, in, out) is det, in,
in, out, in, out) is det.
:- mode set_tree234.foldl2(pred(in, in, out, mdi, muo) is det, in,
in, out, mdi, muo) is det.
:- mode set_tree234.foldl2(pred(in, in, out, di, uo) is det, in,
in, out, di, uo) is det.
:- mode set_tree234.foldl2(pred(in, in, out, in, out) is semidet, in,
in, out, in, out) is semidet.
:- mode set_tree234.foldl2(pred(in, in, out, mdi, muo) is semidet, in,
in, out, mdi, muo) is semidet.
:- mode set_tree234.foldl2(pred(in, in, out, di, uo) is semidet, in,
in, out, di, uo) is semidet.
:- pred set_tree234.fold3(
pred(T1, T2, T2, T3, T3, T4, T4), set_tree234(T1),
T2, T2, T3, T3, T4, T4).
:- mode set_tree234.fold3(pred(in, in, out, in, out, in, out) is det, in,
in, out, in, out, in, out) is det.
:- mode set_tree234.fold3(pred(in, in, out, in, out, mdi, muo) is det, in,
in, out, in, out, mdi, muo) is det.
:- mode set_tree234.fold3(pred(in, in, out, in, out, di, uo) is det, in,
in, out, in, out, di, uo) is det.
:- mode set_tree234.fold3(pred(in, in, out, in, out, in, out) is semidet, in,
in, out, in, out, in, out) is semidet.
:- mode set_tree234.fold3(pred(in, in, out, in, out, mdi, muo) is semidet, in,
in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.fold3(pred(in, in, out, in, out, di, uo) is semidet, in,
in, out, in, out, di, uo) is semidet.
:- pred set_tree234.foldl3(
pred(T1, T2, T2, T3, T3, T4, T4), set_tree234(T1),
T2, T2, T3, T3, T4, T4).
:- mode set_tree234.foldl3(pred(in, in, out, in, out, in, out) is det, in,
in, out, in, out, in, out) is det.
:- mode set_tree234.foldl3(pred(in, in, out, in, out, mdi, muo) is det, in,
in, out, in, out, mdi, muo) is det.
:- mode set_tree234.foldl3(pred(in, in, out, in, out, di, uo) is det, in,
in, out, in, out, di, uo) is det.
:- mode set_tree234.foldl3(pred(in, in, out, in, out, in, out) is semidet, in,
in, out, in, out, in, out) is semidet.
:- mode set_tree234.foldl3(pred(in, in, out, in, out, mdi, muo) is semidet, in,
in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.foldl3(pred(in, in, out, in, out, di, uo) is semidet, in,
in, out, in, out, di, uo) is semidet.
:- pred set_tree234.fold4(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5), set_tree234(T1),
T2, T2, T3, T3, T4, T4, T5, T5).
:- mode set_tree234.fold4(pred(in, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.fold4(pred(in, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.fold4(pred(in, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.fold4(
pred(in, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.fold4(
pred(in, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.fold4(
pred(in, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, di, uo) is semidet.
:- pred set_tree234.foldl4(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5), set_tree234(T1),
T2, T2, T3, T3, T4, T4, T5, T5).
:- mode set_tree234.foldl4(pred(in, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.foldl4(pred(in, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.foldl4(pred(in, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.foldl4(
pred(in, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.foldl4(
pred(in, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.foldl4(
pred(in, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, di, uo) is semidet.
:- pred set_tree234.fold5(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5, T6, T6),
set_tree234(T1), T2, T2, T3, T3, T4, T4, T5, T5, T6, T6).
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.fold5(
pred(in, in, out, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, in, out, di, uo) is semidet.
:- pred set_tree234.foldl5(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5, T6, T6),
set_tree234(T1), T2, T2, T3, T3, T4, T4, T5, T5, T6, T6).
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.foldl5(
pred(in, in, out, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, in, out, di, uo) is semidet.
:- pred set_tree234.fold6(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5, T6, T6, T7, T7),
set_tree234(T1), T2, T2, T3, T3, T4, T4, T5, T5, T6, T6, T7, T7).
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.fold6(
pred(in, in, out, in, out, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, in, out, in, out, di, uo) is semidet.
:- pred set_tree234.foldl6(
pred(T1, T2, T2, T3, T3, T4, T4, T5, T5, T6, T6, T7, T7),
set_tree234(T1), T2, T2, T3, T3, T4, T4, T5, T5, T6, T6, T7, T7).
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, in, out) is det,
in, in, out, in, out, in, out, in, out, in, out, in, out) is det.
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is det,
in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is det.
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, di, uo) is det,
in, in, out, in, out, in, out, in, out, in, out, di, uo) is det.
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, in, out) is semidet,
in, in, out, in, out, in, out, in, out, in, out, in, out) is semidet.
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is semidet,
in, in, out, in, out, in, out, in, out, in, out, mdi, muo) is semidet.
:- mode set_tree234.foldl6(
pred(in, in, out, in, out, in, out, in, out, in, out, di, uo) is semidet,
in, in, out, in, out, in, out, in, out, in, out, di, uo) is semidet.
% all_true(Pred, Set) succeeds iff Pred(Element) succeeds
% for all the elements of Set.
%
:- pred set_tree234.all_true(pred(T)::in(pred(in) is semidet),
set_tree234(T)::in) is semidet.
% Return the set of items for which the predicate succeeds.
%
:- func set_tree234.filter(pred(T)::in(pred(in) is semidet),
set_tree234(T)::in) = (set_tree234(T)::out) is det.
:- pred set_tree234.filter(pred(T)::in(pred(in) is semidet),
set_tree234(T)::in, set_tree234(T)::out) is det.
% Return the set of items for which the predicate succeeds,
% and the set for which it fails.
%
:- pred set_tree234.filter(pred(T)::in(pred(in) is semidet),
set_tree234(T)::in, set_tree234(T)::out, set_tree234(T)::out) is det.
% set_tree234.divide(Pred, Set, TruePart, FalsePart):
% TruePart consists of those elements of Set for which Pred succeeds;
% FalsePart consists of those elements of Set for which Pred fails.
%
:- pred set_tree234.divide(pred(T)::in(pred(in) is semidet),
set_tree234(T)::in, set_tree234(T)::out, set_tree234(T)::out) is det.
% set_tree234.divide_by_set(DivideBySet, Set, InPart, OutPart):
% InPart consists of those elements of Set which are also in
% DivideBySet; OutPart consists of those elements of which are
% not in DivideBySet.
%
:- pred set_tree234.divide_by_set(set_tree234(T)::in, set_tree234(T)::in,
set_tree234(T)::out, set_tree234(T)::out) is det.
%--------------------------------------------------%
%--------------------------------------------------%