struct A { field_a: i32 }

struct B<'a> { field_b: &'a A }

struct C<'b, 'a: 'b> { field_b: &'b mut B<'a> }

trait Tr<'b, 'a> {
    fn field_b(&self) -> &'b B<'a>;
}

impl<'b, 'a> Tr<'b, 'a> for C<'b, 'a> {
    fn field_b(&self) -> &'b B<'a>{
        self.field_b
    }
}


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