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TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passjudge pass (deepseek-v4-pro + gpt-5.6-terra)audited 2026-08-16
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For every n≥16 there is an n-vertex graph with hom⁡(G)<3log⁡2n

Statement

For every integer n≥16, there exists an n-vertex graph G such that hom⁡(G)<3log⁡2n.

Facts & Assumptions

Given: An integer n≥16 and k=⌈3log⁡2n⌉.

[L1]

The homogeneous number of a graph is the larger of its clique and stable-set numbers (Homogeneous vertex sets and the homogeneous number hom⁡(G)=max⁡{ω(G),α(G)}).

[L2]

In G(n,1/2), all possible edges are independent Bernoulli variables on the labelled vertex set [n] (The Erdős-Rényi finite random graph G(n,p)).

[L3]

Prescribing r present edges and s absent edges in G(n,p) has probability pr(1−p)s (A prescribed set of present and absent edges in G(n,p) has product probability).

[L4]

Expectations of a finite family of random variables add without an independence hypothesis (Expectation is linear for every finite family of random variables, without any independence hypothesis).

[L5]

If a nonnegative integer-valued random variable on a finite probability space has expectation below 1, some outcome makes it 0 (The first-moment method for avoiding or forcing a finite count of bad events).

[L7]

For b>0 with b≠1 and x>0, log⁡bx:=log⁡x/log⁡b (The logarithm to a positive base other than one).

[L8]

log⁡:(0,∞)→R is strictly increasing, and for x,y>0 satisfies log⁡(xy)=log⁡x+log⁡y, log⁡(1/x)=−log⁡x, and log⁡1=0 (Order, continuity, range, and the product, quotient, and reciprocal laws for the natural logarithm).

Proof

technique · constructive
1.1L7L8algebra

By [L8], log⁡2>log⁡1=0, so [L7] makes log⁡2=log⁡/log⁡2 strictly increasing with log⁡21=0. Applying log⁡(xy)=log⁡x+log⁡y to the factors of an integer power, and log⁡(1/x)=−log⁡x for a negative exponent, gives log⁡2(2m)=m for every integer m and log⁡2(xj)=jlog⁡2x for every x>0 and every positive integer j.

2.1givenstep 1.1algebra

Since n≥16=24, step 1.1 gives L:=log⁡2n≥4, and k=⌈3L⌉ satisfies k≥3L≥12.

3.1step 2.1L2L3L6

In G(n,1/2) let X count the k-subsets that induce a clique or a stable set. For a fixed k-subset these two disjoint events each prescribe all (k2) pairs, so [L2] and [L3] give probability 2⋅2−(k2).

4.1step 3.1L4L6algebra

By [L4] and [L6], EX=2(nk)2−k(k−1)/2≤2nk2−k(k−1)/2.

5.1step 1.1step 2.1step 4.1algebra

By step 1.1 the base-two logarithm of that last bound is 1+kL−k(k−1)/2=1+k(L−(k−1)/2)≤1+3L(1−L)/2<0, where the first inequality uses k≥3L and L≥4, which make L−(k−1)/2≤(1−L)/2<0. Since log⁡2 is strictly increasing with log⁡21=0, the bound itself is below 1, so EX<1.

6.1step 3.1step 5.1L1L5constructdischarge-construct∎

By [L5], choose an outcome graph G with X=0. It has no homogeneous k-subset, and any homogeneous set of order at least k would contain one, so hom⁡(G)≤k−1<3L=3log⁡2n.

Depends on

Used by

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