@safe unittest{    import std.algorithm.setops;     import std.algorithm.searching : canFind;    import std.range;    import std.typecons : tuple;     auto N = sequence!"n"(0);         // the range of natural numbers    auto N2 = cartesianProduct(N, N); // the range of all pairs of natural numbers     // Various arbitrary number pairs can be found in the range in finite time.    assert(canFind(N2, tuple(0, 0)));    assert(canFind(N2, tuple(123, 321)));    assert(canFind(N2, tuple(11, 35)));    assert(canFind(N2, tuple(279, 172)));} @safe unittest{    import std.algorithm.setops;     import std.algorithm.searching : canFind;    import std.typecons : tuple;     auto B = [ 1, 2, 3 ];    auto C = [ 4, 5, 6 ];    auto BC = cartesianProduct(B, C);     foreach (n; [[1, 4], [2, 4], [3, 4], [1, 5], [2, 5], [3, 5], [1, 6],                 [2, 6], [3, 6]])    {        assert(canFind(BC, tuple(n[0], n[1])));    }} @safe unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;    import std.typecons : tuple;     auto A = [ 1, 2, 3 ];    auto B = [ 'a', 'b', 'c' ];    auto C = [ "x", "y", "z" ];    auto ABC = cartesianProduct(A, B, C);     assert(ABC.equal([        tuple(1, 'a', "x"), tuple(1, 'a', "y"), tuple(1, 'a', "z"),        tuple(1, 'b', "x"), tuple(1, 'b', "y"), tuple(1, 'b', "z"),        tuple(1, 'c', "x"), tuple(1, 'c', "y"), tuple(1, 'c', "z"),        tuple(2, 'a', "x"), tuple(2, 'a', "y"), tuple(2, 'a', "z"),        tuple(2, 'b', "x"), tuple(2, 'b', "y"), tuple(2, 'b', "z"),        tuple(2, 'c', "x"), tuple(2, 'c', "y"), tuple(2, 'c', "z"),        tuple(3, 'a', "x"), tuple(3, 'a', "y"), tuple(3, 'a', "z"),        tuple(3, 'b', "x"), tuple(3, 'b', "y"), tuple(3, 'b', "z"),        tuple(3, 'c', "x"), tuple(3, 'c', "y"), tuple(3, 'c', "z")    ]));} @system unittest{    import std.algorithm.setops;     import std.typecons : tuple, Tuple;     // Figure which number can be found in most arrays of the set of    // arrays below.    double[][] a =    [        [ 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];    auto b = new Tuple!(double, uint)[1];    // it will modify the input range, hence we need to create a duplicate    largestPartialIntersection(a.dup, b);    // First member is the item, second is the occurrence count    assert(b[0] == tuple(7.0, 4u));    // 7.0 occurs in 4 out of 5 inputs, more than any other number     // If more of the top-frequent numbers are needed, just create a larger    // tgt range    auto c = new Tuple!(double, uint)[2];    largestPartialIntersection(a, c);    assert(c[0] == tuple(1.0, 3u));    // 1.0 occurs in 3 inputs     // multiset    double[][] x =    [        [1, 1, 1, 1, 4, 7, 8],        [1, 7],        [1, 7, 8],        [4, 7],        [7]    ];    auto y = new Tuple!(double, uint)[2];    largestPartialIntersection(x.dup, y);    // 7.0 occurs 5 times    assert(y[0] == tuple(7.0, 5u));    // 1.0 occurs 6 times    assert(y[1] == tuple(1.0, 6u));} @system unittest{    import std.algorithm.setops;     import std.typecons : tuple, Tuple;     // Figure which number can be found in most arrays of the set of    // arrays below, with specific per-element weights    double[][] a =    [        [ 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];    auto b = new Tuple!(double, uint)[1];    double[double] weights = [ 1:1.2, 4:2.3, 7:1.1, 8:1.1 ];    largestPartialIntersectionWeighted(a, b, weights);    // First member is the item, second is the occurrence count    assert(b[0] == tuple(4.0, 2u));    // 4.0 occurs 2 times -> 4.6 (2 * 2.3)    // 7.0 occurs 3 times -> 4.4 (3 * 1.1)    // multiset    double[][] x =    [        [ 1, 1, 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];    auto y = new Tuple!(double, uint)[1];    largestPartialIntersectionWeighted(x, y, weights);    assert(y[0] == tuple(1.0, 5u));    // 1.0 occurs 5 times -> 1.2 * 5 = 6} @system unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;     double[][] a =    [        [ 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];    auto witness = [        1, 1, 1, 4, 4, 7, 7, 7, 7, 8, 8    ];    assert(equal(multiwayMerge(a), witness));     double[][] b =    [        // range with duplicates        [ 1, 1, 4, 7, 8 ],        [ 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];    // duplicates are propagated to the resulting range    assert(equal(multiwayMerge(b), witness));} @system unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;     // sets    double[][] a =    [        [ 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 8],        [ 4 ],        [ 7 ],    ];     auto witness = [1, 4, 7, 8];    assert(equal(multiwayUnion(a), witness));     // multisets    double[][] b =    [        [ 1, 1, 1, 4, 7, 8 ],        [ 1, 7 ],        [ 1, 7, 7, 8],        [ 4 ],        [ 7 ],    ];    assert(equal(multiwayUnion(b), witness));     double[][] c =    [        [9, 8, 8, 8, 7, 6],        [9, 8, 6],        [9, 8, 5]    ];    auto witness2 = [9, 8, 7, 6, 5];    assert(equal(multiwayUnion!"a > b"(c), witness2));} @safe unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;    import std.range.primitives : isForwardRange;     //sets    int[] a = [ 1, 2, 4, 5, 7, 9 ];    int[] b = [ 0, 1, 2, 4, 7, 8 ];    assert(equal(setDifference(a, b), [5, 9]));    static assert(isForwardRange!(typeof(setDifference(a, b))));     // multisets    int[] x = [1, 1, 1, 2, 3];    int[] y = [1, 1, 2, 4, 5];    auto r = setDifference(x, y);    assert(equal(r, [1, 3]));    assert(setDifference(r, x).empty);} @safe unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;     // sets    int[] a = [ 1, 2, 4, 5, 7, 9 ];    int[] b = [ 0, 1, 2, 4, 7, 8 ];    int[] c = [ 0, 1, 4, 5, 7, 8 ];    assert(equal(setIntersection(a, a), a));    assert(equal(setIntersection(a, b), [1, 2, 4, 7]));    assert(equal(setIntersection(a, b, c), [1, 4, 7]));     // multisets    int[] d = [ 1, 1, 2, 2, 7, 7 ];    int[] e = [ 1, 1, 1, 7];    assert(equal(setIntersection(a, d), [1, 2, 7]));    assert(equal(setIntersection(d, e), [1, 1, 7]));} @safe unittest{    import std.algorithm.setops;     import std.algorithm.comparison : equal;    import std.range.primitives : isForwardRange;     // sets    int[] a = [ 1, 2, 4, 5, 7, 9 ];    int[] b = [ 0, 1, 2, 4, 7, 8 ];    assert(equal(setSymmetricDifference(a, b), [0, 5, 8, 9][]));    static assert(isForwardRange!(typeof(setSymmetricDifference(a, b))));     //mutisets    int[] c = [1, 1, 1, 1, 2, 2, 2, 4, 5, 6];    int[] d = [1, 1, 2, 2, 2, 2, 4, 7, 9];    assert(equal(setSymmetricDifference(c, d), setSymmetricDifference(d, c)));    assert(equal(setSymmetricDifference(c, d), [1, 1, 2, 5, 6, 7, 9]));}