The sandglass conjecture asserts that every recovering pair 
of families of subsets of an 
-element set satisfies
The power sets of two complementary subsets give equality. Costa (2026) improved the known upper bound to 
, but the conjectured bound remains open.
See also
Power Set,
Recovering
Pair
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References
Costa, S. "An Improved Upper Bound for Recovering Pairs."
2 Oct 2026. https://arxiv.org/abs/2610.03851.
Cite this as:
Weisstein, Eric W. "Sandglass Conjecture."
From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SandglassConjecture.html
Subject classifications
