This is an appealing idea and it took me a moment to see why it wouldn't work (other than the part where you simply don't have enough information). It's correc

This is an appealing idea and it took me a moment to see why it wouldn't work (other than the part where you simply don't have enough information). It's correct to say that the bloom filter will produce no false negatives and the OOABF will produce no false positives, so if your OOABF returns true or your bloom filter returns false then you know for sure whether you've seen the item before. The trouble happens when your OOABF returns false and your bloom filter returns true, in which case you might have seen it before.