diff --git a/Sanchime.Functional/Core/Products/Identity.cs b/Sanchime.Functional/Core/Products/Identity.cs
new file mode 100644
index 0000000..1c5ecf3
--- /dev/null
+++ b/Sanchime.Functional/Core/Products/Identity.cs
@@ -0,0 +1,8 @@
+namespace Sanchime.Functional.Core.Products;
+
+/// <summary>
+/// 单位元
+/// </summary>
+/// <typeparam name="T"></typeparam>
+/// <returns></returns>
+public delegate T Identity<T>();
\ No newline at end of file