Counting-types characterization of NTP2_2

Let φ(x,y)\varphi(x,y) be a partitioned formula, and let fφ(k,l)f_{\varphi}(k,l) denote the number of pairwise-inconsistent partial φ\varphi-types of size kk over a parameter set of size ll. For tinNtin\boldsymbol{N}, let tvarphi\bigwedge_tvarphi denote the associated tt-fold conjunction formula. Counting-types conjecture. The following are equivalent: (i) tvarphi\bigwedge_tvarphi is NTP2_2 for every tinNtin\boldsymbol{N}; (ii) ftvarphi(k,l)f_{\bigwedge_tvarphi}(k,l) is polynomially bounded for every tinNtin\boldsymbol{N}. At minimum, fφ(k,l)f_{\varphi}(k,l) should be polynomially bounded for every formula in an NTP2_2 theory. The paper proves that polynomial boundedness follows from ULCFS and obtains an ε\varepsilon-power-saving result, but the proposed characterization is open.

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Primary source

Artem Chernikov and Chuyin Jiang, “Fractional Helly property and combinatorics of forking in NTP_2 theories”, arXiv:2605.18123 (2026).

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