diff --git a/headers/Concepts.hpp b/headers/Concepts.hpp
new file mode 100644
index 0000000..187ecc3
--- /dev/null
+++ b/headers/Concepts.hpp
@@ -0,0 +1,34 @@
+/*
+ * SPDX-FileCopyrightText: Dora "cat" <cat@thenight.club>
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public License,
+ * v. 2.0. If a copy of the MPL was not distributed with this file, You can
+ * obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef GUARD_TOURMALINE_CONCEPTS_H
+#define GUARD_TOURMALINE_CONCEPTS_H
+#include <concepts>
+#include <functional>
+
+namespace Tourmaline::Concepts {
+template <typename T>
+concept Hashable = std::equality_comparable<T> && requires(T x) {
+  { std::hash<T>{}(x) } -> std::convertible_to<std::size_t>;
+};
+
+template <typename Base, typename Type1, typename Type2>
+concept Either = std::same_as<Base, Type1> || std::same_as<Base, Type2>;
+
+// Oh C++ and your jank
+template <typename Base, typename Type1, typename Type2> struct _opposite_of {
+  using type = std::conditional_t<std::is_same_v<Base, Type1>, Type2, Type1>;
+};
+
+template <typename Base, typename Type1, typename Type2>
+  requires Either<Base, Type1, Type2>
+using OppositeOf = _opposite_of<Base, Type1, Type2>::type;
+
+} // namespace Tourmaline::Concepts
+#endif