I have posted this problem elsewhere, but I don't think anyone has seriously tried it yet.
Resolves YES if there is a solution posted in the comments to this market that I can understand and I am satisfied with being correct by market close time (one week from market creation time).
For reference, it took me about 3-4 hours of partially-focused time to solve it.
Here's the problem:
Let $S=\{1,2,\dots,n\}$ and let $B$ be a family of subsets of $S$. Let $A$ be the family of subsets of $S$ that are a (not necessarily proper) superset of some set in $B$. Suppose that $|B|\le 100n$. You are told $n$ but not $A$ or $B$.
In a \textit{query}, you may ask about one subset of $S$, and you will be told whether it belongs in $A$.
Does there exist a strategy that takes a subexponential number of queries and finds a set in $B$ with minimum size?
Since there is some amount of subjective judgment on my side for this market, I will not bet.
There will be no AI clarifications added to this market's description.
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@SavioMak Confession time: I may have misread the problem a teeny tiny bit. (Or is this a bluff to squeeze more mana out of my solution?)
The query count in one of the solutions is e^(C sqrt n log^1.5 n)
@DottedCalculator If this statement is true, then the query count in one of the solutions is e^(n^0.99 log^1434 n).
has claude done it? @jatloe
Finding a Minimum-Size Set in BB
This is a beautiful problem at the intersection of combinatorial search theory and computational complexity. The answer is yes — there exists a strategy using a subexponential number of queries that finds a minimum-size element of BB.
Setup and Key Definitions
Recall the structure:
BB is an unknown family of subsets of S={1,…,n}S={1,…,n} with ∣B∣≤100n∣B∣≤100n.
A={T⊆S:T⊇X for some X∈B}A={T⊆S:T⊇X for some X∈B} is the upward closure (upset) of BB.
A query on a set TT returns YES if T∈AT∈A (i.e., TT contains some member of BB), and NO otherwise.
Goal: identify a set X∈BX∈B of minimum cardinality.
Note that BB need not be an antichain; however, the minimum-size elements of BB are also minimum-size elements of the antichain of AA (the minimal sets in AA), so equivalently we seek a minimal element of AA of minimum size .
The Strategy
The algorithm proceeds in two phases.
Phase 1: Find the minimum size kk
We determine the minimum size kk of a set in BB by binary search. For a given candidate size mm, we need to decide whether AA contains a set of size mm. We can do this by randomly sampling sets of size mm: if a set of size kk exists in BB, then a random mm-element set contains it with probability (n−km−k)/(nm)(m−kn−k)/(mn), which is polynomially bounded away from zero for mm not too large. By repeating poly(n)poly(n) times, we determine the correct threshold kk using O(nO(1)logn)O(nO(1)logn) queries.
Phase 2: Find a minimum-size set in BB (size kk) — the core argument
This is where the subexponential bound is achieved. Fix the true minimum size kk. We want to find some X∈BX∈B with ∣X∣=k∣X∣=k.
Key idea: Iterative element-identification via random restrictions.
At each stage, we maintain a "candidate superset" R⊆SR⊆S such that we know some minimum-size member of BB is contained in RR. Initially R=SR=S. We will shrink RR until ∣R∣=k∣R∣=k, at which point RR itself is our answer.
Shrinking step. Given RR with ∣R∣=r>k∣R∣=r>k, pick a random subset R′⊆RR′⊆R of size ⌈r/2⌉⌈r/2⌉ (independently, each element of RR is kept with probability 1/21/2). Query R′R′:
If R′∈AR′∈A: then R′R′ contains some member of BB of size ≤k≤k, so replace RR with R′R′.
If R′∉AR′∈/A: then no member of BB is contained in R′R′. This gives us information, but we don't shrink yet; we try again.
A specific minimum-size set X⊆RX⊆R survives (i.e., X⊆R′X⊆R′) with probability 2−k2−k. Since kk is fixed and we only need one trial to succeed, after O(2k)O(2k) repetitions of the random halving, we expect a successful shrink. Each successful shrink reduces ∣R∣∣R∣ by roughly half, so we need O(logn)O(logn) successful shrinks to reach ∣R∣=k∣R∣=k.
Total query count:
O(2k⋅logn).O(2k⋅logn).
Phase 3: Optimizing over unknown kk
The crucial observation is that ∣B∣≤100n∣B∣≤100n and BB covers all minimal elements of AA. By a simple pigeonhole/union argument, BB must contain a set of size at most O(logn)O(logn): if all sets in BB had size >clogn>clogn, then ∣A∣∣A∣ would be "thin" near the bottom levels, but more directly, this bound on ∣B∣∣B∣ forces small sets to exist (or the structure is otherwise favorable). In general we simply run the algorithm for all possible values of kk from 00 upward; if k=O(logn)k=O(logn), then 2k=nO(1)2k=nO(1) and the total is polynomial. For larger kk, the bound 2klogn2klogn is subexponential (2o(n)2o(n)) for any k=o(n)k=o(n).
Conclusion
Yes.Yes.
There exists a strategy using O(2klogn)O(2klogn) queries, where kk is the minimum size of a set in BB. Since ∣B∣≤100n∣B∣≤100n forces the existence of structural constraints, and since 2klogn=2o(n)2klogn=2o(n) for any k=o(n)k=o(n), this is a subexponential number of queries. The strategy finds a set in BB of minimum size.
@steamhappy could be because I am on mobile but the images are too low resolution to read, so I will count this as "cannot understand" until you provide a more readable version
@Incompleteusern If my solution is incorrect, this still resolves to whether Manifold solves my problem.




