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+This error occurs when the compiler is unable to unambiguously infer the
+return type of a function or method which is generic on return type, such
+as the `collect` method for `Iterator`s.
+
+For example:
+
+```compile_fail,E0284
+fn main() {
+    let n: u32 = 1;
+    let mut d: u64 = 2;
+    d = d + n.into();
+}
+```
+
+Here we have an addition of `d` and `n.into()`. Hence, `n.into()` can return
+any type `T` where `u64: Add<T>`. On the other hand, the `into` method can
+return any type where `u32: Into<T>`.
+
+The author of this code probably wants `into()` to return a `u64`, but the
+compiler can't be sure that there isn't another type `T` where both
+`u32: Into<T>` and `u64: Add<T>`.
+
+To resolve this error, use a concrete type for the intermediate expression:
+
+```
+fn main() {
+    let n: u32 = 1;
+    let mut d: u64 = 2;
+    let m: u64 = n.into();
+    d = d + m;
+}
+```