diff --git a/tc/CMakeLists.txt b/tc/CMakeLists.txt
index ee13ab0..294c5ce 100644
--- a/tc/CMakeLists.txt
+++ b/tc/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_library(tc
+    include/tc/pair_map.hpp
     include/tc/core.hpp
     include/tc/cosets.hpp
     include/tc/group.hpp
@@ -9,3 +10,5 @@ add_library(tc
     src/solve.cpp)
 
 target_include_directories(tc PUBLIC include)
+
+add_subdirectory(test)
diff --git a/tc/include/tc/pair_map.hpp b/tc/include/tc/pair_map.hpp
new file mode 100644
index 0000000..614f639
--- /dev/null
+++ b/tc/include/tc/pair_map.hpp
@@ -0,0 +1,453 @@
+#pragma once
+
+#include <algorithm>
+#include <cstddef>
+#include <iterator>
+#include <tuple>
+#include <vector>
+
+namespace tc {
+    template<typename T>
+    struct pair_map {
+        struct iterator;
+        struct const_iterator;
+        struct view;
+        struct const_view;
+
+    private:
+        size_t _size;
+        std::vector<T> _data{};
+
+        static size_t idx(size_t i, size_t j);
+
+    public:
+        explicit pair_map(size_t size);
+
+        explicit pair_map(size_t size, const T &value);
+
+        [[nodiscard]] size_t size() const;
+
+        T &operator()(size_t i, size_t j);
+
+        T operator()(size_t i, size_t j) const;
+
+        view of(size_t f);
+
+        const_view of(size_t f) const;
+
+        const_view cof(size_t f);
+
+        iterator begin();
+
+        iterator end();
+
+        const_iterator begin() const;
+
+        const_iterator end() const;
+
+        const_iterator cbegin();
+
+        const_iterator cend();
+    };
+
+    template<typename T>
+    struct pair_map<T>::iterator {
+        using reference = std::tuple<size_t, size_t, T &>;
+
+    private:
+        pair_map<T> &_map;
+        size_t _i, _j;
+
+    public:
+        iterator(pair_map<T> &map, size_t i, size_t j);
+
+        iterator operator++();
+
+        iterator operator++(int) &;
+
+        reference operator*();
+
+        bool operator!=(const iterator &other);
+    };
+
+    template<typename T>
+    struct pair_map<T>::const_iterator {
+        using value_type = std::tuple<size_t, size_t, T>;
+
+    private:
+        const pair_map<T> &_map;
+        size_t _i, _j;
+
+    public:
+        const_iterator(const pair_map<T> &map, size_t i, size_t j);
+
+        const_iterator operator++();
+
+        const_iterator operator++(int) &;
+
+        value_type operator*();
+
+        bool operator!=(const const_iterator &other);
+    };
+
+    template<typename T>
+    struct pair_map<T>::view {
+        struct iterator;
+        struct const_iterator;
+
+    private:
+        pair_map<T> &_map;
+        size_t _f;
+
+    public:
+        view(pair_map<T> &map, size_t f);
+
+        iterator begin();
+
+        iterator end();
+
+        const_iterator begin() const;
+
+        const_iterator end() const;
+
+        const_iterator cbegin();
+
+        const_iterator cend();
+    };
+
+    template<typename T>
+    struct pair_map<T>::view::iterator {
+        using reference = std::tuple<size_t, size_t, T &>;
+
+    private:
+        pair_map<T> &_map;
+        size_t _f, _v;
+
+    public:
+        iterator(pair_map<T> &map, size_t f, size_t v);
+
+        iterator operator++();
+
+        iterator operator++(int);
+
+        reference operator*();
+
+        bool operator!=(const iterator &other);
+    };
+
+    template<typename T>
+    struct pair_map<T>::view::const_iterator {
+        using value_type = std::tuple<size_t, size_t, T>;
+
+    private:
+        const pair_map<T> &_map;
+        size_t _f, _v;
+
+    public:
+        const_iterator(const pair_map<T> &map, size_t f, size_t v);
+
+        const_iterator operator++();
+
+        const_iterator operator++(int);
+
+        value_type operator*();
+
+        bool operator!=(const const_iterator &other);
+    };
+
+    template<typename T>
+    struct pair_map<T>::const_view {
+        using const_iterator = typename pair_map<T>::view::const_iterator;
+
+    private:
+        const pair_map<T> &_map;
+        size_t _f;
+
+    public:
+        const_view(const pair_map<T> &map, size_t f);
+
+        const_iterator begin() const;
+
+        const_iterator end() const;
+
+        const_iterator cbegin();
+
+        const_iterator cend();
+    };
+
+    // region pair_map
+
+    template<typename T>
+    size_t pair_map<T>::idx(size_t i, size_t j) {
+        if (i < j) std::swap(i, j);
+        return j * (j + 1) / 2 + i;
+    }
+
+    template<typename T>
+    pair_map<T>::pair_map(size_t size)
+        : _size(size), _data(size * (size + 1) / 2) {}
+
+    template<typename T>
+    pair_map<T>::pair_map(size_t size, const T &value)
+        : _size(size), _data(size * (size + 1) / 2, value) {}
+
+    template<typename T>
+    size_t pair_map<T>::size() const {
+        return _size;
+    }
+
+    template<typename T>
+    T &pair_map<T>::operator()(size_t i, size_t j) {
+        return _data[idx(i, j)];
+    }
+
+    template<typename T>
+    T pair_map<T>::operator()(size_t i, size_t j) const {
+        return _data[idx(i, j)];
+    }
+
+    template<typename T>
+    typename pair_map<T>::view pair_map<T>::of(size_t f) {
+        return view(*this, f);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_view pair_map<T>::of(size_t f) const {
+        return const_view(*this, f);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_view pair_map<T>::cof(size_t f) {
+        return const_view(*this, f);
+    }
+
+    template<typename T>
+    typename pair_map<T>::iterator pair_map<T>::begin() {
+        return iterator(*this, 0, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::iterator pair_map<T>::end() {
+        return iterator(*this, 0, _size);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::begin() const {
+        return const_iterator(*this, 0, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::end() const {
+        return const_iterator(*this, 0, _size);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::cbegin() {
+        return const_iterator(*this, 0, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::cend() {
+        return const_iterator(*this, 0, _size);
+    }
+
+    // endregion
+
+    // region pair_map::iterator
+
+    template<typename T>
+    pair_map<T>::iterator::iterator(pair_map<T> &map, size_t i, size_t j)
+        :_map(map), _i(i), _j(j) {}
+
+    template<typename T>
+    typename pair_map<T>::iterator pair_map<T>::iterator::operator++() {
+        if (++_i > _j) {
+            _i = 0;
+            ++_j;
+        }
+        return *this;
+    }
+
+    template<typename T>
+    typename pair_map<T>::iterator pair_map<T>::iterator::operator++(int) &{
+        iterator it = *this;
+        ++this;
+        return it;
+    }
+
+    template<typename T>
+    typename pair_map<T>::iterator::reference pair_map<T>::iterator::operator*() {
+        return std::tie(_i, _j, _map(_i, _j));
+    }
+
+    template<typename T>
+    bool pair_map<T>::iterator::operator!=(const pair_map::iterator &other) {
+        return &_map != &other._map || _i != other._i || _j != other._j;
+    }
+
+    // endregion
+
+    // region pair_map::const_iterator
+
+    template<typename T>
+    pair_map<T>::const_iterator::const_iterator(const pair_map<T> &map, size_t i, size_t j)
+        :_map(map), _i(i), _j(j) {}
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::const_iterator::operator++() {
+        if (++_i > _j) {
+            _i = 0;
+            ++_j;
+        }
+        return *this;
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator pair_map<T>::const_iterator::operator++(int) &{
+        const_iterator it = *this;
+        ++this;
+        return it;
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_iterator::value_type pair_map<T>::const_iterator::operator*() {
+        return std::tuple(_i, _j, _map(_i, _j));
+    }
+
+    template<typename T>
+    bool pair_map<T>::const_iterator::operator!=(const pair_map::const_iterator &other) {
+        return &_map != &other._map || _i != other._i || _j != other._j;
+    }
+
+    // endregion
+
+    // region pair_map::view
+
+    template<typename T>
+    pair_map<T>::view::view(pair_map<T> &map, size_t f)
+        : _map(map), _f(f) {}
+
+    template<typename T>
+    typename pair_map<T>::view::iterator pair_map<T>::view::begin() {
+        return iterator(_map, _f, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::iterator pair_map<T>::view::end() {
+        return iterator(_map, _f, _map._size);
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::begin() const {
+        return const_iterator(_map, _f, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::end() const {
+        return const_iterator(_map, _f, _map._size);
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::cbegin() {
+        return const_iterator(_map, _f, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::cend() {
+        return const_iterator(_map, _f, _map._size);
+    }
+
+    // endregion
+
+    // region pair_map::view::iterator
+
+    template<typename T>
+    pair_map<T>::view::iterator::iterator(pair_map<T> &map, size_t f, size_t v)
+        : _map(map), _f(f), _v(v) {}
+
+    template<typename T>
+    typename pair_map<T>::view::iterator pair_map<T>::view::iterator::operator++() {
+        ++_v;
+        return *this;
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::iterator pair_map<T>::view::iterator::operator++(int) {
+        iterator it = *this;
+        ++this;
+        return it;
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::iterator::reference pair_map<T>::view::iterator::operator*() {
+        auto [i, j] = std::minmax(_f, _v);
+        return std::tie(i, j, _map(i, j));
+    }
+
+    template<typename T>
+    bool pair_map<T>::view::iterator::operator!=(const pair_map::view::iterator &other) {
+        return &_map != &other._map || _f != other._f || _v != other._v;
+    }
+
+    // endregion
+
+    // region pair_map::view::const_iterator
+
+    template<typename T>
+    pair_map<T>::view::const_iterator::const_iterator(const pair_map<T> &map, size_t f, size_t v)
+        : _map(map), _f(f), _v(v) {}
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::const_iterator::operator++() {
+        ++_v;
+        return *this;
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator pair_map<T>::view::const_iterator::operator++(int) {
+        const_iterator it = *this;
+        ++this;
+        return it;
+    }
+
+    template<typename T>
+    typename pair_map<T>::view::const_iterator::value_type pair_map<T>::view::const_iterator::operator*() {
+        auto [i, j] = std::minmax(_f, _v);
+        return std::tuple(i, j, _map(i, j));
+    }
+
+    template<typename T>
+    bool pair_map<T>::view::const_iterator::operator!=(const pair_map::view::const_iterator &other) {
+        return &_map != &other._map || _f != other._f || _v != other._v;
+    }
+
+    // endregion
+
+    // region pair_map::const_view
+
+    template<typename T>
+    pair_map<T>::const_view::const_view(const pair_map<T> &map, size_t f)
+        : _map(map), _f(f) {}
+
+    template<typename T>
+    typename pair_map<T>::const_view::const_iterator pair_map<T>::const_view::begin() const {
+        return const_iterator(_map, _f, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_view::const_iterator pair_map<T>::const_view::end() const {
+        return const_iterator(_map, _f, _map._size);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_view::const_iterator pair_map<T>::const_view::cbegin() {
+        return const_iterator(_map, _f, 0);
+    }
+
+    template<typename T>
+    typename pair_map<T>::const_view::const_iterator pair_map<T>::const_view::cend() {
+        return const_iterator(_map, _f, _map._size);
+    }
+    
+    // endregion
+}
diff --git a/tc/src/keep.cpp b/tc/src/keep.cpp
new file mode 100644
index 0000000..4020e10
--- /dev/null
+++ b/tc/src/keep.cpp
@@ -0,0 +1 @@
+#include <tc/pair_map.hpp>
diff --git a/tc/test/CMakeLists.txt b/tc/test/CMakeLists.txt
new file mode 100644
index 0000000..e9621bd
--- /dev/null
+++ b/tc/test/CMakeLists.txt
@@ -0,0 +1,13 @@
+add_executable(grouptests grouptest.cpp)
+target_link_libraries(grouptests PUBLIC tc)
+
+add_test(NAME GroupIterateRef COMMAND grouptests iterate_ref)
+set_tests_properties(GroupIterateRef PROPERTIES TIMEOUT 30)
+add_test(NAME GroupIterateConst COMMAND grouptests iterate_const)
+set_tests_properties(GroupIterateConst PROPERTIES TIMEOUT 30)
+add_test(NAME GroupIterate COMMAND grouptests iterate)
+set_tests_properties(GroupIterate PROPERTIES TIMEOUT 30)
+add_test(NAME GroupView COMMAND grouptests view)
+set_tests_properties(GroupView PROPERTIES TIMEOUT 30)
+
+add_custom_target(alltests DEPENDS grouptests)
diff --git a/tc/test/grouptest.cpp b/tc/test/grouptest.cpp
new file mode 100644
index 0000000..4c9c562
--- /dev/null
+++ b/tc/test/grouptest.cpp
@@ -0,0 +1,94 @@
+#include <functional>
+#include <iostream>
+#include <unordered_map>
+
+#include <tc/pair_map.hpp>
+
+int iterate_ref() {
+    tc::pair_map<size_t> pm(4, 2);
+
+    for (auto [i, j, m]: pm) {
+        m = i + j;
+    }
+
+    for (auto [i, j, m]: pm) {
+        std::cout << "(" << i << "," << j << ") = " << m << std::endl;
+    }
+
+    return EXIT_SUCCESS;
+}
+
+int iterate_const() {
+    tc::pair_map<size_t> pm(4, 2);
+    for (const auto &[i, j, m]: pm) {
+        m = i + j;
+    }
+
+    const tc::pair_map<size_t> pmc = pm;
+    for (auto [i, j, m]: pmc) {
+        std::cout << "(" << i << "," << j << ") = " << m << std::endl;
+    }
+
+    return EXIT_SUCCESS;
+}
+
+int iterate() {
+    tc::pair_map<size_t> pm(4, 2);
+
+    std::cout << pm(0, 0) << std::endl;
+    pm(0, 0) = 3;
+    std::cout << pm(0, 0) << std::endl;
+
+    for (auto [i, j, m]: pm) {
+        std::cout << i << " " << j << " = " << m << std::endl;
+    }
+
+    std::cout << pm(1, 0) << " " << pm(0, 1) << std::endl;
+    pm(1, 0) = 7;
+    std::cout << pm(1, 0) << " " << pm(0, 1) << std::endl;
+    pm(0, 1) = 9;
+    std::cout << pm(1, 0) << " " << pm(0, 1) << std::endl;
+
+    return EXIT_SUCCESS;
+}
+
+int view() {
+    tc::pair_map<size_t> pm(4, 2);
+
+    for (int i = 0; i < 4; ++i) {
+        for (int j = i; j < 4; ++j) {
+            pm(i, j) = i + j;
+        }
+    }
+
+    std::cout << "ALL:" << std::endl;
+    for (auto [i, j, m]: pm) {
+        std::cout << "  (" << i << "," << j << ") = " << m << std::endl;
+    }
+
+    std::cout << "VIEW:" << std::endl;
+    for (auto [i, j, m]: pm.of(2)) {
+        std::cout << "  (" << i << "," << j << ") = " << m << std::endl;
+    }
+
+    return EXIT_SUCCESS;
+}
+
+static std::unordered_map<std::string, std::function<int()>> tests = {
+    {"iterate_ref",   iterate_ref},
+    {"iterate_const", iterate_const},
+    {"iterate",       iterate},
+    {"view",          view},
+};
+
+int main(int argc, char *argv[]) {
+    std::vector<std::string> args(argv + 1, argv + argc);
+
+    auto it = tests.find(args[0]);
+    if (it == tests.end()) {
+        std::cout << "Test not found" << std::endl;
+        return EXIT_FAILURE;
+    }
+    auto test = it->second;
+    return test();
+}