A recovering pair is a pair of nonempty families of subsets
of the same finite set such that
implies
and
implies
for every
and
. Each member of either
family can therefore be recovered from its set difference
with a member of the other family.
For an -element
ground set, Costa (2026) proved
The sandglass conjecture predicts the stronger bound . Costa (2026) states that ChatGPT generated initial
versions of the retained proofs and computational code under his research strategy,
and that he independently verified all retained claims.