error[E0276]: impl has stricter requirements than trait
  --> $DIR/traits-misc-mismatch-2.rs:23:5
   |
19 |     fn zip<B, U: Iterator<U>>(self, other: U) -> ZipIterator<Self, U>;
   |     ------------------------------------------------------------------ definition of `zip` from trait
...
23 |     fn zip<B, U: Iterator<B>>(self, other: U) -> ZipIterator<T, U> {
   |     ^ impl has extra requirement `U: Iterator<B>`

error: aborting due to previous error