diff --git a/Guidelines.md b/Guidelines.md
index fab576b..824c28b 100644
--- a/Guidelines.md
+++ b/Guidelines.md
@@ -920,6 +920,18 @@ using c4 = cartesian_product_t<std::integer_sequence<int, 1, 2>, std::integer_se
 // c3 == std::tuple<int, char, int, float, double ,char, double, float>
 // c4 == std::integer_sequence<int, 1, 3, 1, 4, 1, 5, 2, 3, 2, 4, 2, 5>
 
+// descartes product
+std::vector<int> v1 { 1, 2, 3, 4 };
+std::vector<float> v2 { 9.8f, 4.4f };
+std::vector<std::string> v3 { "r", "g", "b" };
+
+descartes_product([](int x, float y, const std::string& z)
+{
+    std::cout << x << " " << y << " " << z << std::endl;
+}, v1, v2, v3);
+
+// print elements from v1 x v2 x v3
+
 // matrix operatings
 using matrix = std::tuple<std::tuple<char,   int,    double>,
                           std::tuple<char,   double, int>,
diff --git a/README.md b/README.md
index 063b2eb..900f079 100644
--- a/README.md
+++ b/README.md
@@ -5,6 +5,7 @@
 ## Overview
 ```cpp
 #include <monster.hpp>
+
 using namespace monster;
 
 int main(int argc, char* argv[])
diff --git a/Tutorial.md b/Tutorial.md
index c62205f..72e5622 100644
--- a/Tutorial.md
+++ b/Tutorial.md
@@ -1564,12 +1564,20 @@ int main(int argc, char* argv[])
     {
         [](float i){ std::cout << "float " << i << std::endl; },
         [](double d){ std::cout << "double " << d << std::endl; },
-        [](const auto& s){ std::cout << "string " << s << std::endl; }
+        [](const std::string& s){ std::cout << "string " << s << std::endl; }
     };
 
     for (auto&& v : to_range(tup))
          std::visit(show, v);
 
+    std::any a = 7;
+
+    a = float(1.98);
+    any_visit(show, a);
+
+    a = std::string("[]<template auto ...>(){}();");
+    any_visit(show, a);
+
     capture_invoke(pf)(1, 2, 3);
     capture_invoke(pf, 3)(1, 2);
 
@@ -1951,6 +1959,15 @@ int main(int argc, char* argv[])
     is_identical<is_subset_v<std::tuple<float, char, double>,
             std::tuple<int, double, char, float, char, double, int>>>();
 
+    std::vector<int> v1 { 1, 2, 3, 4 };
+    std::vector<float> v2 { 9.8f, 4.4f };
+    std::vector<std::string> v3 { "r", "g", "b" };
+
+    descartes_product([](int x, float y, const std::string& z)
+    {
+        std::cout << x << " " << y << " " << z << std::endl;
+    }, v1, v2, v3);
+
     is_identical<cartesian_product_t<std::tuple<int, double>, std::tuple<char, float>>,
             std::tuple<int, char, int, float, double ,char, double, float>>();
     is_identical<cartesian_product_t<std::integer_sequence<int, 1, 2>, std::integer_sequence<int, 3, 4, 5>>,
diff --git a/example/monster.cpp b/example/monster.cpp
index 3233b40..26db34e 100644
--- a/example/monster.cpp
+++ b/example/monster.cpp
@@ -1957,6 +1957,15 @@ int main(int argc, char* argv[])
     is_identical<is_subset_v<std::tuple<float, char, double>,
             std::tuple<int, double, char, float, char, double, int>>>();
 
+    std::vector<int> v1 { 1, 2, 3, 4 };
+    std::vector<float> v2 { 9.8f, 4.4f };
+    std::vector<std::string> v3 { "r", "g", "b" };
+
+    descartes_product([](int x, float y, const std::string& z)
+    {
+        std::cout << x << " " << y << " " << z << std::endl;
+    }, v1, v2, v3);
+
     is_identical<cartesian_product_t<std::tuple<int, double>, std::tuple<char, float>>,
             std::tuple<int, char, int, float, double ,char, double, float>>();
     is_identical<cartesian_product_t<std::integer_sequence<int, 1, 2>, std::integer_sequence<int, 3, 4, 5>>,
diff --git a/include/monster.hpp b/include/monster.hpp
index be6d9e8..3c5389b 100644
--- a/include/monster.hpp
+++ b/include/monster.hpp
@@ -5500,8 +5500,13 @@ namespace monster
 
         using F::operator()...;
 
+        consteval decltype(auto) operator()(auto) const
+        {
+            static_assert(false, "unsupported type");
+        }
+
         template <typename T>
-        decltype(auto) operator()(std::reference_wrapper<T> r)
+        constexpr decltype(auto) operator()(std::reference_wrapper<T> r)
         {
             return (*this)(r.get());
         }
@@ -5758,7 +5763,7 @@ namespace monster
     requires std::is_aggregate_v<T>
     constexpr decltype(auto) aggregate_fields_count()
     {
-        decltype(auto) [...Args] = T();
+        auto [...Args] = T();
 
         return sizeof...(Args);
     }
@@ -5766,7 +5771,7 @@ namespace monster
     template <typename T>
     constexpr decltype(auto) aggregate_to_tuple(T&& t)
     {
-        decltype(auto) [...Args] = t;
+        auto& [...Args] = t;
 
         return std::forward_as_tuple(std::forward<decltype(Args)>(Args)...);
     }
@@ -6793,6 +6798,16 @@ namespace monster
         (integer_sequence_t<size_t, j - i, i, 1>());
     }
 
+    template <typename F, typename... Args>
+    constexpr decltype(auto) transform_as_tuple(F&& f, const std::tuple<Args...>& t)
+    {
+        return [&]<size_t... N>(const std::index_sequence<N...>&)
+        {
+            return std::tuple<std::result_of_t<F(Args)>...>(std::forward<F>(f)(std::get<N>(t))...);
+        }
+        (std::index_sequence_for<Args...>());
+    }
+
     template <typename F, typename... Args>
     constexpr decltype(auto) tuple_adjacent_transform(F&& f, const std::tuple<Args...>& t)
     {
@@ -8551,6 +8566,47 @@ namespace monster
     template <typename T, typename U>
     using cartesian_product_t = typeof_t<cartesian_product<T, U>>;
 
+    template <size_t N, typename... Args>
+    constexpr decltype(auto) next_iterator(std::tuple<Args...>& t, std::tuple<Args...>& b, std::tuple<Args...>& e)
+    {
+        auto& i = ++std::get<N>(t);
+
+        if constexpr(N != 0)
+        {
+            if (i == std::get<N>(e))
+            {
+                i = std::get<N>(b);
+                next_iterator<N - 1>(t, b, e);
+            }
+        }
+    }
+
+    template <typename F, typename... Args>
+    requires (sizeof...(Args) > 0)
+    constexpr decltype(auto) descartes_product(F&& f, Args&&... args)
+    {
+        constexpr auto N = sizeof...(Args);
+        auto reference = []<typename I>(I&& i) -> decltype(auto) { return *i; };
+
+        bool empty = false;
+        auto tuple = std::forward_as_tuple(std::forward<Args>(args)...);
+
+        tuple_for_each(tuple, [&]<typename T>(T&& t)
+        {
+            if (!empty && t.begin() == t.end())
+                empty = true;
+        });
+
+        if (!empty)
+        {
+            auto b = std::make_tuple(std::forward<Args>(args).begin()...);
+            auto e = std::make_tuple(std::forward<Args>(args).end()...);
+
+            for (auto t = b; std::get<0>(t) != std::get<0>(e); next_iterator<N - 1>(t, b, e))
+                 std::apply(f, transform_as_tuple(reference, t));
+        }
+    }
+
     template <typename T, typename U>
     struct large_number_multiplier
     {
diff --git a/include/version.hpp b/include/version.hpp
index eb0b0d8..2e3ea52 100644
--- a/include/version.hpp
+++ b/include/version.hpp
@@ -20,7 +20,7 @@
  *   time a set of code changes is merged to the master branch.
  */
 
-#define MONSTER_VERSION_NUMBER 309
+#define MONSTER_VERSION_NUMBER 310
 #define MONSTER_VERSION_STRING "Monster/" MONSTER_STRINGIZE(MONSTER_VERSION_NUMBER)
 
 #endif