enum Ast<'a> {
    Num(usize),
    Add(&'a Ast<'a>, &'a Ast<'a>)
}

fn mk_add_bad1<'a,'b>(x: &'a Ast<'a>, y: &'b Ast<'b>) -> Ast<'a> {
    Ast::Add(x, y) //~ ERROR lifetime mismatch [E0623]
}

fn main() {
}