Commit 2025-10-06 12:30 abf8c9d3
View on Github →feat(Topology/Algebra/InfiniteSum): generalise to allow summation filters (#29914)
We introduce a notion of a "summation filter" on a type, which is (a structure wrapper around) a filter on the finsets of that type. Then we can define tsums / tprods "along L" for any summation filter L, giving a formalism that specializes to the existing notion of unconditional summation, but also covers conditional summation on ℕ etc. This is implemented using an optional parameter to HasSum, tsum etc which defaults to the standard unconditional sum, so the vast majority of existing code using unconditional summation will work without change.
Co-authored by Chris Birkbeck.