lemmaroutine

Choice of hierarchy parameters K, L, k

Lemma·bud:parameters·§5.1 Parameters, rare levels, and histories

Statement (paper)

There are integers K,L,k→∞K,L,k\to\infty such that Klog⁡L=o(log⁡t),D/K=o(1),kKlog⁡L=o(log⁡t),k20((D/K)1/4+L−1+S−1+dQ,min⁡−1)=o(1).\begin{aligned} K\log L&=o(\log t),& D/K&=o(1),\\ kK\log L&=o(\log t),& k^{20}\left((D/K)^{1/4}+L^{-1}+S^{-1}+d_{Q,\min}^{-1}\right)&=o(1). \end{aligned} Set ϵ=k−1/16\epsilon=k^{-1/16} and et=(D/K)1/4+L−1e_t=(D/K)^{1/4}+L^{-1}. Then k3/S=o(1)k^3/S=o(1), k3+1/16et=o(1)k^{3+1/16}e_t=o(1), and k=to(1)k=t^{o(1)}.

In plain English

There are integers K,L,k→∞K,L,k\to\infty with Klog⁡L=o(log⁡t)K\log L=o(\log t), D/K=o(1)D/K=o(1), kKlog⁡L=o(log⁡t)kK\log L=o(\log t), and k20((D/K)1/4+L−1+S−1+dQ,min⁡−1)=o(1)k^{20}\big((D/K)^{1/4}+L^{-1}+S^{-1}+d_{Q,\min}^{-1}\big)=o(1). With ϵ=k−1/16\epsilon=k^{-1/16} and et=(D/K)1/4+L−1e_t=(D/K)^{1/4}+L^{-1}, this gives k3/S=o(1)k^3/S=o(1), k3+1/16et=o(1)k^{3+1/16}e_t=o(1) and k=to(1)k=t^{o(1)}.

Why it's here

This fixes the parameters once and for all, so later arguments can treat kk, KK, LL as growing slowly enough to absorb error terms. The tradeoff is that KK, LL and kk grow, but only slowly relative to log⁡t\log t, while k20k^{20} times the error terms (D/K)1/4(D/K)^{1/4}, L−1L^{-1}, S−1S^{-1} and dQ,min⁡−1d_{Q,\min}^{-1} still tends to 0. The budget estimates and the popular-circle deletion use this to show their error terms are o(1)o(1) or o(S)o(S).
Classified routine:
Standard diagonal choice of slowly growing parameters: since D, S, d_{Q,min} and log t are given sequences with the appropriate growth, one picks K, L, k tending to infinity slowly enough that each listed quantity is o(1). This is pure bookkeeping with no new idea.

Sources

PaperOpen
Section
§5.1 Parameters, rare levels, and histories
Page
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Label
bud:parameters
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sections/04-budgets.tex:27
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