diff --git a/libs/group/CMakeLists.txt b/libs/group/CMakeLists.txt
new file mode 100644
index 00000000..7a2b0a31
--- /dev/null
+++ b/libs/group/CMakeLists.txt
@@ -0,0 +1,7 @@
+file(GLOB_RECURSE PSEMEK_GROUP_HEADERS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" "include/*.hpp")
+
+psemek_add_library(psemek-group ${PSEMEK_GROUP_HEADERS})
+target_include_directories(psemek-group PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
+target_link_libraries(psemek-group PUBLIC psemek-util)
+
+psemek_glob_tests(psemek-group tests)
diff --git a/libs/group/include/psemek/group/cyclic.hpp b/libs/group/include/psemek/group/cyclic.hpp
new file mode 100644
index 00000000..601d3340
--- /dev/null
+++ b/libs/group/include/psemek/group/cyclic.hpp
@@ -0,0 +1,124 @@
+#pragma once
+
+#include <psemek/util/range.hpp>
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+#include <limits>
+
+namespace psemek::group
+{
+
+	template <std::size_t N, typename Repr = std::size_t>
+	struct cyclic
+	{
+		static_assert(std::is_integral_v<Repr> && std::is_unsigned_v<Repr>);
+		static_assert(std::numeric_limits<Repr>::max() > N);
+
+		static constexpr std::size_t size()
+		{
+			return N;
+		}
+
+		cyclic() = default;
+
+		static cyclic identity()
+		{
+			return cyclic{};
+		}
+
+		static cyclic rotation(Repr const & value)
+		{
+			return cyclic{value % static_cast<Repr>(N)};
+		}
+
+		template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
+		static cyclic rotation(T const & value)
+		{
+			if (value >= 0)
+				return cyclic{static_cast<Repr>(static_cast<std::size_t>(value) % N)};
+			else
+			{
+				auto r = (static_cast<std::int64_t>(value) % static_cast<std::int64_t>(N));
+				return cyclic{static_cast<Repr>((r < 0) ? r + static_cast<std::int64_t>(N) : r)};
+			}
+		}
+
+		Repr value() const
+		{
+			return repr_;
+		}
+
+		struct value_iterator
+		{
+			using difference_type = int;
+			using value_type = cyclic<N, Repr>;
+			using pointer = value_type *;
+			using reference	= value_type &;
+			using iterator_category = std::forward_iterator_tag;
+
+			Repr repr;
+
+			cyclic<N, Repr> operator *() const
+			{
+				return cyclic<N, Repr>{repr};
+			}
+
+			value_iterator & operator++()
+			{
+				++repr;
+				return *this;
+			}
+
+			friend bool operator == (value_iterator const & it1, value_iterator const & it2)
+			{
+				return it1.repr == it2.repr;
+			}
+		};
+
+		static auto values()
+		{
+			return util::range{value_iterator{0}, value_iterator{N}};
+		}
+
+	private:
+		Repr repr_{0};
+
+		explicit cyclic(Repr const & repr)
+			: repr_(repr)
+		{}
+	};
+
+	template <std::size_t N, typename Repr>
+	bool operator == (cyclic<N, Repr> const & g1, cyclic<N, Repr> const & g2)
+	{
+		return g1.value() == g2.value();
+	}
+
+	template <std::size_t N, typename Repr>
+	auto operator <=> (cyclic<N, Repr> const & g1, cyclic<N, Repr> const & g2)
+	{
+		return g1.value() <=> g2.value();
+	}
+
+	template <std::size_t N, typename Repr>
+	cyclic<N, Repr> operator * (cyclic<N, Repr> const & g1, cyclic<N, Repr> const & g2)
+	{
+		return cyclic<N, Repr>::rotation(g1.value() + g2.value());
+	}
+
+	template <std::size_t N, typename Repr>
+	cyclic<N, Repr> inverse(cyclic<N, Repr> const & g)
+	{
+		return cyclic<N, Repr>::rotation(N - g.value());
+	}
+
+	template <typename OStream, std::size_t N, typename Repr>
+	OStream & operator << (OStream & os, cyclic<N, Repr> const & g)
+	{
+		os << 'C' << N << "(r" << static_cast<std::size_t>(g.value()) << ")";
+		return os;
+	}
+
+}
diff --git a/libs/group/include/psemek/group/dihedral.hpp b/libs/group/include/psemek/group/dihedral.hpp
new file mode 100644
index 00000000..33899469
--- /dev/null
+++ b/libs/group/include/psemek/group/dihedral.hpp
@@ -0,0 +1,177 @@
+#pragma once
+
+#include <psemek/group/cyclic.hpp>
+
+#include <cstddef>
+#include <type_traits>
+#include <limits>
+
+namespace psemek::group
+{
+
+	template <std::size_t N, typename Repr = std::size_t>
+	struct dihedral
+	{
+		static_assert(std::is_integral_v<Repr> && std::is_unsigned_v<Repr>);
+		static_assert(std::numeric_limits<Repr>::max() > N);
+
+		static constexpr std::size_t size()
+		{
+			return 2 * N;
+		}
+
+		dihedral() = default;
+
+		static dihedral identity()
+		{
+			return dihedral{};
+		}
+
+		static dihedral rotation(Repr const & repr)
+		{
+			return dihedral{repr % static_cast<Repr>(N)};
+		}
+
+		template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
+		static dihedral rotation(T const & value)
+		{
+			if (value >= 0)
+				return dihedral{static_cast<Repr>(static_cast<std::size_t>(value) % N)};
+			else
+			{
+				auto r = (static_cast<std::int64_t>(value) % static_cast<std::int64_t>(N));
+				return dihedral{static_cast<Repr>((r < 0) ? r + static_cast<std::int64_t>(N) : r)};
+			}
+		}
+
+		template <typename Repr2>
+		static dihedral rotation(cyclic<N, Repr2> const & value)
+		{
+			return dihedral{static_cast<Repr>(value.repr())};
+		}
+
+		static dihedral reflection(Repr repr)
+		{
+			return dihedral{(repr % static_cast<Repr>(N)) + static_cast<Repr>(N)};
+		}
+
+		template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
+		static dihedral reflection(T const & value)
+		{
+			if (value >= 0)
+				return dihedral{static_cast<Repr>((static_cast<std::size_t>(value) % N) + N)};
+			else
+			{
+				auto r = (static_cast<std::int64_t>(value) % static_cast<std::int64_t>(N));
+				return dihedral{static_cast<Repr>((r < 0) ? r + static_cast<std::int64_t>(2 * N) : r + static_cast<std::int64_t>(N))};
+			}
+		}
+
+		Repr value() const
+		{
+			return repr_;
+		}
+
+		bool is_rotation() const
+		{
+			return repr_ < N;
+		}
+
+		bool is_reflection() const
+		{
+			return repr_ >= N;
+		}
+
+		struct value_iterator
+		{
+			using difference_type = int;
+			using value_type = dihedral<N, Repr>;
+			using pointer = value_type *;
+			using reference	= value_type &;
+			using iterator_category = std::forward_iterator_tag;
+
+			Repr repr;
+
+			dihedral<N, Repr> operator *() const
+			{
+				return dihedral<N, Repr>{repr};
+			}
+
+			value_iterator & operator++()
+			{
+				++repr;
+				return *this;
+			}
+
+			friend bool operator == (value_iterator const & it1, value_iterator const & it2)
+			{
+				return it1.repr == it2.repr;
+			}
+		};
+
+		static auto values()
+		{
+			return util::range{value_iterator{0}, value_iterator{2 * N}};
+		}
+
+	private:
+		Repr repr_{0};
+
+		explicit dihedral(Repr const & repr)
+			: repr_(repr)
+		{}
+	};
+
+	template <std::size_t N, typename Repr>
+	bool operator == (dihedral<N, Repr> const & g1, dihedral<N, Repr> const & g2)
+	{
+		return g1.value() == g2.value();
+	}
+
+	template <std::size_t N, typename Repr>
+	auto operator <=> (dihedral<N, Repr> const & g1, dihedral<N, Repr> const & g2)
+	{
+		return g1.value() <=> g2.value();
+	}
+
+	template <std::size_t N, typename Repr>
+	dihedral<N, Repr> operator * (dihedral<N, Repr> const & g1, dihedral<N, Repr> const & g2)
+	{
+		if (g1.is_rotation())
+		{
+			auto repr = g1.value() + g2.value();
+			if (g2.is_rotation())
+				return dihedral<N, Repr>::rotation(repr);
+			else
+				return dihedral<N, Repr>::reflection(repr);
+		}
+		else
+		{
+			auto repr = g1.value() + static_cast<Repr>(N) - g2.value();
+			if (g2.is_rotation())
+				return dihedral<N, Repr>::reflection(repr);
+			else
+				return dihedral<N, Repr>::rotation(repr);
+		}
+	}
+
+	template <std::size_t N, typename Repr>
+	dihedral<N, Repr> inverse(dihedral<N, Repr> const & g)
+	{
+		if (g.is_rotation())
+			return dihedral<N, Repr>::rotation(N - g.value());
+		else
+			return g;
+	}
+
+	template <typename OStream, std::size_t N, typename Repr>
+	OStream & operator << (OStream & os, dihedral<N, Repr> const & g)
+	{
+		if (g.is_rotation())
+			os << 'D' << N << "(r" << static_cast<std::size_t>(g.value()) << ")";
+		else
+			os << 'D' << N << "(s" << (static_cast<std::size_t>(g.value()) % N) << ")";
+		return os;
+	}
+
+}
diff --git a/libs/group/tests/cyclic.cpp b/libs/group/tests/cyclic.cpp
new file mode 100644
index 00000000..39547a68
--- /dev/null
+++ b/libs/group/tests/cyclic.cpp
@@ -0,0 +1,43 @@
+#include <psemek/test/test.hpp>
+
+#include <psemek/group/cyclic.hpp>
+
+#include <set>
+
+using namespace psemek::group;
+
+using group_type = cyclic<7, std::uint8_t>;
+
+test_case(group_cyclic_construct)
+{
+	expect_equal(group_type::identity().value(), 0);
+
+	int const n = group_type::size();
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::rotation(i).value(), i % n);
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::rotation(i - 4 * n).value(), i % n);
+}
+
+test_case(group_cyclic_values)
+{
+	std::set<group_type> values;
+	for (auto g : group_type::values())
+		values.insert(g);
+	expect_equal(values.size(), group_type::size());
+}
+
+test_case(group_cyclic_multiply)
+{
+	for (auto g1 : group_type::values())
+		for (auto g2 : group_type::values())
+				expect_equal(g1 * g2, group_type::rotation(g1.value() + g2.value()));
+}
+
+test_case(group_cyclic_inverse)
+{
+	for (auto g : group_type::values())
+		expect_equal(g * inverse(g), group_type::identity());
+}
diff --git a/libs/group/tests/dihedral.cpp b/libs/group/tests/dihedral.cpp
new file mode 100644
index 00000000..580bdd79
--- /dev/null
+++ b/libs/group/tests/dihedral.cpp
@@ -0,0 +1,62 @@
+#include <psemek/test/test.hpp>
+
+#include <psemek/group/dihedral.hpp>
+
+#include <set>
+
+using namespace psemek::group;
+
+using group_type = dihedral<7, std::uint8_t>;
+
+test_case(group_dihedral_construct)
+{
+	expect_equal(group_type::identity().value(), 0);
+
+	int const n = group_type::size() / 2;
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::rotation(i).value(), i % n);
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::reflection(i).value(), (i % n) + n);
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::rotation(i - 4 * n).value(), i % n);
+
+	for (int i = 0; i < 4 * n; ++i)
+		expect_equal(group_type::reflection(i - 4 * n).value(), (i % n) + n);
+}
+
+test_case(group_dihedral_values)
+{
+	std::set<group_type> values;
+	for (auto g : group_type::values())
+		values.insert(g);
+	expect_equal(values.size(), group_type::size());
+}
+
+test_case(group_dihedral_multiply)
+{
+	for (auto g1 : group_type::values())
+	{
+		for (auto g2 : group_type::values())
+		{
+			auto value = g1.is_rotation() ? g1.value() + g2.value() : g1.value() + group_type::size() / 2 - g2.value();
+
+			if (g1.is_reflection() ^ g2.is_reflection())
+			{
+				expect_equal(g1 * g2, group_type::reflection(value));
+			}
+			else
+			{
+				expect_equal(g1 * g2, group_type::rotation(value));
+			}
+		}
+	}
+}
+
+test_case(group_dihedral_inverse)
+{
+	for (auto g : group_type::values())
+		expect_equal(g * inverse(g), group_type::identity());
+}