{"ast_node_type":"other","tokens":[{"end":64,"kind":"keyword","start":0,"text":"Some(new_a_principal.map_bound(|trait_ref|"}]}
                    Some(new_a_principal.map_bound(|trait_ref| {
                    b_region,
                        ty::ExistentialTraitRef::erase_self_ty(cx, trait_ref)