The combinatorial non-crossing-sums inequality

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Let k1,k2,k3k_1,k_2,k_3 be odd natural numbers. For each i=1,2,3i=1,2,3, let yi,1,…,yi,kiy_{i,1},\ldots,y_{i,k_i} be distinct real numbers, and set yi,0=yi,ki+1=−∞y_{i,0}=y_{i,k_i+1}=-\infty. For two finite pairs of real numbers, call their sums non-crossing when the two sums of one choice and the two sums of the other choice do not alternate in order. Assume:

  1. For each 1≤i≤31\le i\le3 and 0≤p<q≤ki0\le p<q\le k_i of the same parity, the pairs {yi,p,yi,p+1}\{y_{i,p},y_{i,p+1}\} and {−yi,q,−yi,q+1}\{-y_{i,q},-y_{i,q+1}\} have non-crossing sums.
  2. For 0≤pi≤ki0\le p_i\le k_i of the same parity, the three pairs {y1,p1,y1,p1+1}\{y_{1,p_1},y_{1,p_1+1}\}, {y2,p2,y2,p2+1}\{y_{2,p_2},y_{2,p_2+1}\}, and {y3,p3,y3,p3+1}\{y_{3,p_3},y_{3,p_3+1}\} have non-crossing sums.

Combinatorial formulation conjecture. Then

∑i=13∑j=1ki(−1)j−1yi,j<0.\sum_{i=1}^3\sum_{j=1}^{k_i}(-1)^{j-1}y_{i,j}<0.

This is an almost purely combinatorial formulation of the symmetric area inequality. It is stated as an open conjecture in the paper.

References

Primary source

Terence Tao, “An integration approach to the Toeplitz square peg problem”, arXiv:1611.07441 (2017).

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