The hash changes are based on some tests with `arti` and various
specific queries, aimed at reducing the false positive rate.
Sorting the query elements so that generics always come first is
instead aimed at reducing the number of Map operations on mgens,
assuming if the bloom filter does find a false positive, it'll
be able to reject the row without having to track a mapping.
- https://hur.st/bloomfilter/?n=3&p=&m=96&k=6
Different functions have different amounts of inputs, and
unification isn't very slow anyway, so figuring out a single
ideal number of hash functions is nasty, but 6 keeps things
low even up to 10 inputs.
- https://web.archive.org/web/20210927123933/https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.72.2442&rep=rep1&type=pdf
This is the `h1` and `h2`, both derived from `h0`.
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