Trace extension conjecture for forbidden posets

Let PP be a poset, let e(P)e(P) be the largest integer kk such that, for every jj and nn, the family

i=1k([n]j+i)\bigcup_{i=1}^k\binom{[n]}{j+i}

is PP-free, and let Trnk(n,P)Tr_{n-k}(n,P) denote the maximum size of a family whose traces on every (nk)(n-k)-subset are PP-free. Trace extension conjecture. For every integer k<e(P)k<e(P),

Trnk(n,P)=(e(P)k+o(1))(nn/2).Tr_{n-k}(n,P)=(e(P)-k+o(1))\binom{n}{\lfloor n/2\rfloor}.

Moreover, if ke(P)k\ge e(P), then

Trnk(n,P)=o((nn/2)).Tr_{n-k}(n,P)=o\left(\binom{n}{\lfloor n/2\rfloor}\right).

This generalizes the preceding conjecture from ordinary forbidden subposet problems to traces. The displayed lower bound comes from consecutive levels, while the matching asymptotics and the vanishing assertion remain conjectural.

Sources & referencesView supporting material

Primary source

Dániel Gerbner, Balázs Patkós and Máté Vizer, “Forbidden subposet problems for traces of set families”, arXiv:1706.01212 (2017).

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