/// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
/// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
/// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
/// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
/// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
/// over the inner binder (remember that we count De Bruijn indices from 1). However, in the