Paper II visual guide · Visual 22 of 24 · MODEL H / EXACT TELESCOPING, EXPLICIT GROWTH

A small defect can grow under powers

Traditional paper: Theorem 11.1 (p. 37), Corollary 11.3 (p. 38)

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Choose an invertible coordinate shear but independently keep the same numerical operator at both levels:

\[ C=\begin{pmatrix}1&\varepsilon\\0&1\end{pmatrix},\quad T_f=T_c={\operatorname{diag}}(1,2),\quad \varepsilon=\frac1{16}. \]

Then \(\Delta=CT_f-T_cC=\varepsilon E_{01}\). Exact coordinate invertibility has not forced these independently selected operators to intertwine.

Actual power defects and certified upper bounds
Original drawing. Read the description below; expand the labels and data for selectable text.

Reading the drawing

The plotted exact integer heights have the local defect coefficient divided out. The upper estimates can exceed the actual errors and do not imply a uniform bound in time.

Drawing labels and data 20 labels

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  • \(1\)
  • \(1\)
  • \(1\)
  • \(3\)
  • \(4\)
  • \(2\)
  • \(7\)
  • \(12\)
  • \(3\)
  • \(15\)
  • \(32\)
  • \(4\)
  • \(31\)
  • \(80\)
  • \(5\)
  • \(63\)
  • \(192\)
  • \(6\)
  • number of applications \(n\)

Black: \(16\|\text{actual defect}\|_\infty\); pale: certified majorant.

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Evidence note from the source edition

Actual defects and certified upper bounds in the induced infinity norm, both divided by \(\varepsilon\). All heights are exact integers. The upper estimate is valid but need not be tight.

Direct multiplication gives

\[ CT_f^n-T_c^nC=\varepsilon(2^n-1)E_{01}. \]

The general telescoping formula explains every contribution:

\[ CT_f^n-T_c^nC =\sum_{k=0}^{n-1}T_c^{n-1-k}\Delta T_f^k. \]

Since both operator norms are two, the source theorem bounds the error by \(n2^{n-1}\varepsilon\). It does not promise a uniform-in-\(n\) small error merely because \(\varepsilon\) is small.

Had we chosen the transported operator \(T_c'=CT_fC^{-1}\), the defect would be zero and every polynomial action would intertwine exactly. That is a different choice of coarse operator, not a stronger conclusion from the faulty one.

Read this as

Separate coordinate coherence from operator consistency. A defect from one step is propagated by the dynamics on both sides. The telescoping identity tells you exactly how.

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