Re: [PATCH] Add caching to use_reduce,

Sounds good, here's an updated patch that uses frozenset instead.  I
also moved the lru_cache imports up with the other system imports and
renamed use_reduce_cached to _use_reduce_cached to fit with the existing
convention.

Memory usage and performance are essentially unchanged due to the tuple to
frozenset change.

Thanks,
Chun-Yu