The following code fails to compile: ``` rust pub trait Even { fn say(&self); } impl <'a, E: Even> Even for &'a mut E { fn say(&self) { } } pub trait Odd { fn say(&self); } fn print_odd<O: Odd>(o: &mut O) { o.say(); } fn main() { } ``` with the error: ``` foo9.rs:14:5: 14:12 error: failed to find an implementation of trait Even for O foo9.rs:14 o.say(); ^~~~~~~ ```