# Amphicheiral knot polynomials KT-1-H5-to-H6

## Setting

You are solving a mathematical proof problem. Assume only the stated starting checkpoint result and establish the stated target result. Check its hypotheses when applying it. Prove any other intermediate claims you need. End with a clear proof, or identify any gap you cannot close.

## Problem

H5: Let \(K\subset S^3\) be an oriented knot admitting a finite-order orientation-reversing diffeomorphism of \(S^3\) that preserves the orientation of \(K\). Let \(\nabla_K(z)\in\mathbb Z[z]\) be its Conway polynomial, normalized by \(\nabla_{\rm unknot}=1\).
There exists \(f\in\mathbb Z[z]\) such that
\[
\nabla_K(z)\equiv f(z)f(-z)\pmod4,
\]
where the congruence is coefficientwise.

Prove H6: A knot \(K\subset S^3\) is called amphicheiral if an orientation-reversing homeomorphism of \(S^3\) maps \(K\) to itself; the homeomorphism may preserve or reverse the knot orientation.
For every amphicheiral knot \(K\), including the unknot, there exists \(f\in\mathbb Z[z]\) such that
\[
\nabla_K(z)\equiv f(z)f(-z)\pmod4.
\]
Here \(\nabla_K\) is the Conway polynomial normalized by \(\nabla_{\rm unknot}=1\), and the congruence is coefficientwise.

Write the full proof to answer.md in the workspace root. Write the statements and hypotheses of any external results you cite to cited_results.md; if none are used, write 'No external results cited.' Identify any gap you cannot close.