THM0035canonicalv1Removable Singularity
Removable Singularity: two tower-coherent functions agreeing at depth d0 for all inputs agree at all depths <= d0. Repackaging of the Identity Theorem in extension language. The thin set is removable.
Payload
Removable Singularity
Removable Singularity: two tower-coherent functions agreeing at depth d0 for all inputs agree at all depths <= d0. Repackaging of the Identity Theorem in extension language. The thin set is removable.
Removable Singularity
Summary
Removable Singularity: two tower-coherent functions agreeing at depth d0 for all inputs agree at all depths <= d0. Repackaging of the Identity Theorem in extension language. The thin set is removable.
Statement
%
\label{thm:removable-singularity}
Let $K \subseteq \mathbb{L}$ be primordially thin
(Definition~\ref{def:primorial-thinness}, I.D67),
$f \in \mathrm{HolFun}$ bounded on $\mathbb{L} \setminus K$.
Then $f$ extends uniquely to
$\tilde{f} \in \mathrm{Hol}(\mathbb{L})$
(Definition~\ref{def:hol-L}, I.D49):
\[
\boxed{%
K \text{ thin},\;
f \in \mathrm{HolFun}(\mathbb{L} \setminus K)
\text{ bounded}
\;\;\Longrightarrow\;\;
\exists!\; \tilde{f} \in \mathrm{Hol}(\mathbb{L}):\;
\tilde{f}\!\big|_{\mathbb{L} \setminus K} = f.}
\]
Proof / Justification
\textbf{Existence.}
For $t \in K$, define $\tilde{f}(t) \bmod M_d$
by CRT extension (Lemma~\ref{lem:crt-extension}, I.L08)
at each depth $d$.
For $t \notin K$, set $\tilde{f}(t) := f(t)$.
The sequence $(\tilde{f}(t) \bmod M_d)_{d \geq 1}$
is compatible: the CRT reconstruction at $M_{d+1}$
reduces to the one at $M_d$ by transitivity of CRT.
Boundedness of $f$ ensures the reconstructed values
remain in $\hat{\mathbb{Z}}_\tau$.
The extension satisfies tower coherence
(Definition~\ref{def:tower-coherence}, I.D46)
and CRT coherence
(Theorem~\ref{thm:crt-coherence}, I.T18)
by construction, so $\tilde{f}$ is $\tau$-holomorphic.
\textbf{Uniqueness.}
Two extensions $\tilde{f}_1, \tilde{f}_2$
agree on $\mathbb{L} \setminus K$.
Since $K$ is thin,
$\mathbb{L} \setminus K$ is primordially dense,
so $\tilde{f}_1$ and $\tilde{f}_2$ agree at some depth $d_0$.
By the $\tau$-Identity Theorem
(Theorem~\ref{thm:tau-identity}, I.T21),
$\tilde{f}_1 = \tilde{f}_2$.
Source Context
- Registry source:
book-01.jsonlline 153 - Manuscript source:
2nd-edition/book-i-categorical-foundations/02_mainmatter/part16/ch61-thinness.texlines 192-210
Lean / Formalization Notes
- Formalization:
formalized - Module:
TauLib.BookI.Holomorphy.Thinness - Name:
Tau.Holomorphy.removable_singularity
Dependencies
- Canonical: I.D67, I.L08, I.T21
Related Results
Generated by later projection phases.
Related Publications
Generated by later projection phases.
Revision Notes
- 2026-04-24: Initial pilot migration.
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I.T30removable-singularitythm:removable-singularityRelease lines
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