Frankl–Kupavskii stability conjecture for bounded matching number

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Let n,k,tn,k,t be positive integers with n>ktn>kt. Let FF be a kk-graph of order nn. For a hypergraph FF, write u(F) u(F) for its matching number, τ(F)\tau(F) for its vertex-cover number, and e(F)e(F) for its number of edges. For i∈[k]i\in [k], let

Ai(k)(n,t)={A∈([n]k):∣A∩[(t+1)i−1]∣≥i},{\cal A}_i^{(k)}(n,t)=\left\{A\in {[n]\choose k}: \left|A\cap [(t+1)i-1]\right|\ge i\right\},

and let

H(k)(n,t)={e∈([n]k):e∩[t−1]≠∅}∪{[t+k]∖[t]}∪{e∈([n]k):e∩[t]=t,e∩([t+k]∖[t])≠∅}.{\cal H}^{(k)}(n,t)=\left\{e\in {[n]\choose k}:e\cap [t-1]\ne\emptyset\right\}\cup\left\{[t+k]\setminus [t]\right\}\cup\left\{e\in {[n]\choose k}:e\cap [t]=\\{t\\},\\ e\cap ([t+k]\setminus [t])\ne\emptyset\right\}.

Frankl–Kupavskii stability conjecture. If ν(F)≤t\nu(F)\le t, then τ(F)≤t\tau(F)\le t or

e(F)≤max⁡e(A2(k)(n,t)),…,e(Ak(k)(n,t)),e(H(k)(n,t)).e(F)\le\max\\{e({\cal A}_2^{(k)}(n,t)),\dots,e({\cal A}_k^{(k)}(n,t)),e({\cal H}^{(k)}(n,t))\\}.

This is a stability strengthening of the Erdős Matching Conjecture, asserting that a kk-graph with matching number at most tt either has a cover of size at most tt or is bounded by the extremal non-cover constructions. The supplied text gives no resolution status for this conjecture.

References

Primary source

Hongliang Lu, Yan Wang and Xingxing Yu, “On stability of rainbow matchings”, arXiv:2302.06146 (2023).

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