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The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
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These labels describe origin, not correctness: citations and verification chips remain separate evidence.
Nikiforov: for every and every there is such that every graph with has an -restricted vertex set of size at least
Statement
Fix a graph with and a real . Then there exists such that every nonempty finite simple graph with
has an -restricted vertex set of size at least .
Facts & Assumptions
Given: A graph with vertices and a real .
For each , the self-regular-subset theorem gives a constant such that every nonempty graph on vertices has a subset with and -regular (Every finite graph has a linearly large -self-regular vertex subset, -regular pairs and self-regular vertex sets).
The induced counting constants include , and if , , is -regular, and its self-density lies between and , then (A large -self-regular set whose density lies between and forces at least induced copies of ).
A low-density -regular set has a large sparse subset, and a high-density one has a large dense subset, with the explicit parameters supplied by Deleting the high-degree vertices of a -self-regular set of density leaves more than of it, and that remainder is -sparse and Deleting the low-degree vertices of a -self-regular set of density leaves more than of it, and that remainder is -dense.
Every nonempty set of at most two vertices is -restricted, hence -restricted (Sparsity is preserved when the parameter grows, and every nonempty set of at most two vertices is -restricted).
Proof
Set and choose so small that and from [L2]. Then , and the dense trimming parameter from [L3] is also at most , because , , and .
If , the induced-copy hypothesis is never satisfied: both sides of its displayed inequality are . Thus suppose . Let be the constant of [L1], let and be the constants of [L2], put , and set Then and depends only on and .
Now let be a nonempty graph on vertices with . If , then any singleton is -restricted by [L4] and satisfies , because . Hence suppose . By [L1] choose with such that is -regular.
If , then [L2] gives , contrary to the hypothesis on . Therefore either or .
In the first case, the low-density trimming lemma in [L3] yields a subset with that is -sparse by step 1.1. In the second case, the high-density trimming lemma in [L3] yields a subset with the same size bound that is -dense. In either case is -restricted.
Step 3.1 handles small , and steps 4.1 and 5.1 handle all remaining cases, so every graph satisfying the induced-copy bound has an -restricted set of size at least .
Depends on
- $c$-sparse, $c$-dense and $c$-restricted vertex sets
- Every finite graph has a linearly large $\epsilon$-self-regular vertex subset
- An $\epsilon$-regular pair is $\epsilon'$-regular for every $\epsilon'\ge\epsilon$ with $\epsilon'>0$
- A large $\gamma$-self-regular set whose density lies between $\eta$ and $1-\eta$ forces at least $c|W|^{|V(H)|}$ induced copies of $H$
- Deleting the high-degree vertices of a $\gamma$-self-regular set of density $d$ leaves more than $(1-\gamma)$ of it, and that remainder is $((d+\gamma)/(1-\gamma))$-sparse
- Deleting the low-degree vertices of a $\gamma$-self-regular set of density $d$ leaves more than $(1-\gamma)$ of it, and that remainder is $((1-d+2\gamma)/(1-\gamma))$-dense
- Sparsity is preserved when the parameter grows, and every nonempty set of at most two vertices is $0$-restricted
- The induced-embedding count $\operatorname{ind}_H(G)$
- $\epsilon$-regular pairs and self-regular vertex sets
- Edge counts and densities between nonempty vertex sets
- Real powers for positive bases, with the zero-base positive-exponent convention
- The exponential definition of real powers agrees with the existing rational powers
Used by
- A linearly large induced subgraph of a graph with few induced copies again has a linearly large restricted set Corollary
- Rödl: for every H and every ε∈(0,1/2) there is δ>0 such that every nonempty H-free graph has an ε-restricted vertex set of size at least δ|V(G)| Corollary
- What this proof gives for δ, and why the regularity route is expensive Remark
Dependency tree · two levels
30 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Y. Huang, Q. Ju, and X. Zhou, Erdős-Hajnal beyond the five-vertex path, Theorem 1.2 (standard reference, not scraped)