An alternate (and very slightly more efficient) spelling would be:
```
SELECT EXISTS (
WITH found(id) AS NOT MATERIALIZED
(
SELECT self_hash_id
FROM causal
WHERE self_hash_id == ?2
UNION ALL
SELECT parent_id
FROM causal_parent
JOIN found
ON found.id == causal_id
)
SELECT id
FROM found
WHERE id == ?1
)
;
```