A way to refer to the "outer" query implicitly?

My code constructs some queries by passing in constraint clauses like
 type = 'A'

However one of the constraint clauses is
 exists (select 1 from othertable where x = outertable.x)

This works fine, but requires that the caller know that the table being
queried will be "outertable". Is there any way in a subquery used like this to
implicitly reference fields from the outer query?

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greg