failing to be sized?

ex.rs

trait A {
    fn one(&self);
}

trait B {
    fn two(&self);
}

/** Dies because it wants the "Sized" trait
impl<'a> B for A + 'a {
    fn two(&self) {
        self.one()
    }
}

<anon>:10:1: 14:2 error: the trait `core::kinds::Sized` is not implemented for the type `A+'a`
<anon>:10 impl<'a> B for A + 'a {
<anon>:11     fn two(&self) {
<anon>:12         self.one()
<anon>:13     }
<anon>:14 }
<anon>:10:1: 14:2 note: the trait `core::kinds::Sized` must be implemented because it is required by `B`
<anon>:10 impl<'a> B for A + 'a {
<anon>:11     fn two(&self) {
<anon>:12         self.one()
<anon>:13     }
<anon>:14 }
**/

// this doesn't work for me, because B is defined in a different crate
impl<T: A> B for T {
    fn two(&self) {
        self.one()
    }
}

fn main() {
    println!("Hello, world!")
}