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+An attempt was made to retrieve an associated type, but the type was ambiguous.
+
+Erroneous code example:
+
+```compile_fail,E0221
+trait T1 {}
+trait T2 {}
+
+trait Foo {
+    type A: T1;
+}
+
+trait Bar : Foo {
+    type A: T2;
+    fn do_something() {
+        let _: Self::A;
+    }
+}
+```
+
+In this example, `Foo` defines an associated type `A`. `Bar` inherits that type
+from `Foo`, and defines another associated type of the same name. As a result,
+when we attempt to use `Self::A`, it's ambiguous whether we mean the `A` defined
+by `Foo` or the one defined by `Bar`.
+
+There are two options to work around this issue. The first is simply to rename
+one of the types. Alternatively, one can specify the intended type using the
+following syntax:
+
+```
+trait T1 {}
+trait T2 {}
+
+trait Foo {
+    type A: T1;
+}
+
+trait Bar : Foo {
+    type A: T2;
+    fn do_something() {
+        let _: <Self as Bar>::A;
+    }
+}
+```