1

Let $TREE(n)$ and $tree(n)$ are Kruskal' tree sequences. The second one is called weak.

Prove that $TREE(3)>tree^{tree^{tree^{tree^{tree^{8}(7)}(7)}(7)}(7)}(7)$

You can see that inequality in every article about $TREE(3)$ and always it is left without proof.

My real purpose is to prove that $TREE(3)>G64$ but i was only managed to prove that $tree(n)\ge 2^{n}$

Please inform me if there are simpler "combination" (with proof) of weak tree sequence so that it is still lower than $TREE(3)$ and greater than Graham's number.

mkultra
  • 1,382
  • In respect of your "real purpose" ... At https://mathoverflow.net/a/95588/20307 there is a proof that $$\text{TREE(3)} > H_{\vartheta (\Omega^{\omega}, 0)}(n(4))$$ where $H_{\alpha}$ is a version of the Hardy hierarchy and $n()$ is Friedman's block-subsequence function, so the RHS is clearly greater than $G_{64}$. – r.e.s. Nov 27 '19 at 21:50

1 Answers1

2

That is a consequence of @Deedlit's excellent answer here, which proves that $$\text{TREE}(3)>\text{tree}_3(\text{tree}_2(\text{tree}(8)))$$ where $\text{tree}_2(n)=\text{tree}^n(n)$ and $\text{tree}_3(n)={\text{tree}_2}^n(n).$

Thus, letting $N=\text{tree}_2(\text{tree}(8))$, we have $$\begin{align}\text{TREE}(3)&>\text{tree}_3(\text{tree}_2(\text{tree}(8)))=\text{tree}_3(N)\\ &>>\text{tree}^{\text{tree}^{\text{tree}^{\text{...}^{\text{tree}^{N}(N)}{...}}(N)}(N)}(N)\quad\text{with $N$ levels}\\ &>> \text{tree}^{\text{tree}^{\text{tree}^{\text{tree}^{\text{tree}^{8}(7)}(7)}(7)}(7)}(7)\quad\text{with $5$ levels}\end{align}.$$

Definitions:

  1. $\text{TREE}(n)$ is defined as the length of a longest sequence of trees $T_1,T_2,\ldots$, with vertices labelled from ${1, 2, ..., n}$ such that, for all $i,$ $T_i$ has at most $i$ vertices, and for all $i,j$ such that $i<j,$ there is no label-preserving homeomorphic embedding from $T_i$ into $T_j.$

  2. $\text{tree}(n)$ is defined as the length of a longest sequence of unlabelled trees $T_1,T_2,\ldots$, such that, for all $i$, $T_i$ has at most $n+i$ vertices, and for all $i,j$ with $i<j,$ $T_i$ is not homeomorphically embeddable into $T_j.$

r.e.s.
  • 14,371