connective N1 rare writtenliterary
をおいてほかに(は)〜ない — no one/nothing but ~
をおいてほかに(は)〜ない
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Jengo shows をおいてほかに(は)〜ない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Advanced Japanese Grammar. Editorial confidence: low.