All corrections for first lecture acording MB tips done
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@ -183,9 +183,9 @@ $S = \begin{pmatrix}
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\Rightarrow \text{trefoil is not trivial.}
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\]
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\end{example}
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\begin{fact}
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\begin{lemma}
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$\Delta_K(t)$ is symmetric.
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\end{fact}
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\end{lemma}
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\begin{proof}
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Let $S$ be an $n \times n$ matrix.
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\begin{align*}
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@ -152,21 +152,21 @@ A knot (link) is called alternating if it admits an alternating diagram.
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\begin{definition}
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A reducible crossing in a knot diagram is a crossing for which we can find a circle such that its intersection with a knot diagram is exactly that crossing. A knot diagram without reducible crossing is called reduced.
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\end{definition}
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\begin{fact}
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\begin{lemma}
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Any reduced alternating diagram has minimal number of crossings.
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\end{fact}
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\end{lemma}
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\begin{definition}
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The writhe of the diagram is the difference between the number of positive and negative crossings.
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\end{definition}
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\begin{fact}[Tait]
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\begin{lemma}[Tait]
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Any two diagrams of the same alternating knot have the same writhe.
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\end{fact}
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\begin{fact}
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\end{lemma}
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\begin{lemma}
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An alternating knot has Alexander polynomial of the form:
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$
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a_1t^{n_1} + a_2t^{n_2} + \dots + a_s t^{n_s}
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$, where $n_1 < n_2 < \dots < n_s$ and $a_ia_{i+1} < 0$.
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\end{fact}
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\end{lemma}
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\begin{problem}[open]
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What is the minimal $\alpha \in \mathbb{R}$ such that if $z$ is a root of the Alexander polynomial of an alternating knot, then $\Re(z) > \alpha$.\\
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Remark: alternating knots have very simple knot homologies.
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@ -49,20 +49,20 @@ H_1(\widetilde{X}, \mathbb{Z}[t, t^{-1}]) \times
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H_1(\widetilde{X}, \mathbb{Z}[t, t^{-1}]) \longrightarrow \quot{\mathbb{Q}}{\mathbb{Z}[t, t^{-1}]}
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\end{align*}
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\begin{fact}
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\begin{lemma}
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\begin{align*}
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&H_1(\widetilde{X}, \mathbb{Z}[t, t^{-1}]) \cong
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\quot{\mathbb{Z}{[t, t^{-1}]}^n}{(tV - V^T)\mathbb{Z}[t, t^{-1}]^n}\;, \\
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&\text{where $V$ is a Seifert matrix.}
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\end{align*}
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\end{fact}
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\begin{fact}
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\end{lemma}
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\begin{lemma}
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\begin{align*}
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H_1(\widetilde{X}, \mathbb{Z}[t, t^{-1}]) \times
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H_1(\widetilde{X}, \mathbb{Z}[t, t^{-1}]) &\longrightarrow \quot{\mathbb{Q}}{\mathbb{Z}[t, t^{-1}]}\\
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(\alpha, \beta) \quad &\mapsto \alpha^{-1}{(t -1)(tV - V^T)}^{-1}\beta
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\end{align*}
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\end{fact}
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\end{lemma}
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\noindent
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Note that $\mathbb{Z}[t, t^{-1}]$ is not PID.
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Therefore we don't have primary decomposition of this module.
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107
lec_25_02.tex
107
lec_25_02.tex
@ -17,12 +17,12 @@ are shown respectively in
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\begin{figure}[h]
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\centering
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\begin{subfigure}{0.3\textwidth}
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\begin{subfigure}{0.45\textwidth}
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\centering
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\includegraphics[width=0.5\textwidth]
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{unknot.png}
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\end{subfigure}
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\begin{subfigure}{0.3\textwidth}
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\begin{subfigure}{0.45\textwidth}
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\centering
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\includegraphics[width=0.5\textwidth]
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{trefoil.png}
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@ -34,22 +34,24 @@ are shown respectively in
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\begin{figure}[h]
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\centering
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\begin{subfigure}{0.3\textwidth}
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\begin{subfigure}{0.45\textwidth}
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\centering
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\includegraphics[width=0.5\textwidth]
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{not_injective_knot.png}
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\end{subfigure}
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\begin{subfigure}{0.3\textwidth}
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\begin{subfigure}{0.45\textwidth}
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\centering
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\includegraphics[width=0.5\textwidth]
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{not_smooth_knot.png}
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\end{subfigure}
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\caption{Not-knots examples:
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an image of
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a function ${S^1\longrightarrow S^3}$
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that isn't injective (left) and
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of a function
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that isn't smooth (right).}
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\caption{
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Not-knots examples:
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an image of
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a function ${S^1\longrightarrow S^3}$
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that is not injective (left) and
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of a function
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that is not smooth (right).
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}
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\label{fig:notknot}
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\end{figure}
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@ -101,23 +103,40 @@ are shown respectively in
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in $S^3$.
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\end{definition}
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\begin{example}
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Links:
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\begin{itemize}
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\item
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a trivial link with $3$ components:
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\includegraphics[width=0.2\textwidth]{3unknots.png},
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\item
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a Hopf link: \includegraphics[width=0.13\textwidth]{Hopf.png},
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\item
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a Whitehead link:
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\includegraphics[width=0.13\textwidth]{WhiteheadLink.png},
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\item
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a Borromean link:
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\includegraphics[width=0.1\textwidth]{BorromeanRings.png}.
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\end{itemize}
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\end{example}
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%
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\noindent
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Example of simple links are shown in
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\autoref{fig:links}.
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\begin{figure}[h]
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\centering
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\begin{subfigure}{0.5\textwidth}
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\centering
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\includegraphics[width=1\textwidth]
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{3unknots.png}
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\caption{A trivial link with $3$ components.}
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\end{subfigure}
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\begin{subfigure}{0.4\textwidth}
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\centering
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\includegraphics[width=0.7\textwidth]
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{Hopf.png}
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\caption{A Hopf link.}
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\end{subfigure}
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\begin{subfigure}{0.4\textwidth}
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\centering
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\includegraphics[width=0.8\textwidth]
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{WhiteheadLink.png},
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\caption{A Whitehead link.}
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\end{subfigure}
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\begin{subfigure}{0.4\textwidth}
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\centering
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\includegraphics[width=0.7\textwidth]
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{BorromeanRings.png}
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\caption{A Borromean link.}
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\end{subfigure}
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\caption{Link examples.}
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\label{fig:links}
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\end{figure}
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%
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%
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\begin{definition}\label{def:link_diagram}
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@ -133,12 +152,24 @@ a Borromean link:
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\item there are no triple point.
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\end{enumerate}
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\end{definition}
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\noindent
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By \Cref{def:link_diagram} the following pictures can not be a part of a diagram:
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\includegraphics[width=0.05\textwidth]{LinkDiagram1.png},
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\includegraphics[width=0.03\textwidth]{LinkDiagram2.png},
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\includegraphics[width=0.05\textwidth]{LinkDiagram3.png}.
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\begin{figure}[H]
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\centering
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\begin{subfigure}{0.1\textwidth}
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\includegraphics[width=0.8\textwidth]
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{LinkDiagram1.png},
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\end{subfigure}
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\begin{subfigure}{0.1\textwidth}
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\includegraphics[width=0.6\textwidth]
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{LinkDiagram2.png},
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\end{subfigure}
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\begin{subfigure}{0.1\textwidth}
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\includegraphics[width=0.8\textwidth]
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{LinkDiagram3.png}.
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\end{subfigure}
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\end{figure}
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\noindent
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There are under- and overcrossings (tunnels and bridges) on a link diagrams with an obvious meaning.
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@ -152,7 +183,9 @@ We can distinguish two types of crossings: right-handed
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$\left(\PICorientpluscross\right)$, called a positive crossing, and left-handed $\left(\PICorientminuscross\right)$, called a negative crossing.
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\subsection{Reidemeister moves}
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A Reidemeister move is one of the three types of operation on a link diagram as shown below:
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\begin{enumerate}[label=\Roman*]
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\item\hfill\\
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\includegraphics[width=0.6\textwidth]{rm1.png},
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@ -179,8 +212,10 @@ A Reidemeister move is one of the three types of operation on a link diagram as
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%Authors: Arnold, V.I., Varchenko, Alexander, Gusein-Zade, S.M.
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\subsection{Seifert surface}
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\noindent
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Let $D$ be an oriented diagram of a link $L$. We change the diagram by smoothing each crossing:
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Let $D$ be an oriented diagram of a link $L$.
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We change the diagram by smoothing each crossing:
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\begin{align*}
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\PICorientpluscross \mapsto
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\PICorientLRsplit,\\
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@ -192,7 +227,8 @@ a disjoint union of circles on the plane.
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Each circle bounds a disks in
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$\mathbb{R}^3$
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(we choose disks that don't intersect).
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For each smoothed crossing we add a twisted band: right-handed for a positive and left-handed for a negative one.
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For each smoothed crossing we add a twisted band:
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right-handed for a positive and left-handed for a negative one.
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We get an orientable surface $\Sigma$
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such that $\partial \Sigma = L$.\\
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@ -208,6 +244,7 @@ such that $\partial \Sigma = L$.\\
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\end{figure}
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\noindent
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Note: the obtained surface isn't unique and in general doesn't need to be connected, but by taking connected sum of all components we can easily get a connected surface (i.e. we take two disconnected components and cut a disk in each of them: $D_1$ and $D_2$. Then we glue both components on the boundaries: $\partial D_1$ and $\partial D_2$.
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\begin{figure}[h]
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@ -312,13 +349,13 @@ Seifert surfaces of minimal genus
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\label{fig:unknot}
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\end{figure}
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\begin{fact}
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\begin{lemma}
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$
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g_3(\Sigma) = \frac{1}{2} b_1 (\Sigma) =
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\frac{1}{2} \dim_{\mathbb{R}}H_1(\Sigma, \mathbb{R}),
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$
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where $b_1$ is first Betti number of a surface $\Sigma$.
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\end{fact}
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\end{lemma}
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\subsection{Seifert matrix}
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Let $L$ be a link and
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@ -2,8 +2,8 @@
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\begin{fact}[Milnor Singular Points of Complex Hypersurfaces]
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\end{fact}
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\begin{lemma}[Milnor Singular Points of Complex Hypersurfaces]
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\end{lemma}
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%\end{comment}
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\noindent
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An oriented knot is called negative amphichiral if the mirror image $m(K)$ of $K$ is equivalent the reverse knot of $K$: $K^r$. \\
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@ -58,14 +58,12 @@
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{\newline}{}%
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\theoremstyle{break}
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\newtheorem{lemma}{Lemma}[section]
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\newtheorem{fact}{Fact}[section]
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\newtheorem{corollary}{Corollary}[section]
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\newtheorem{proposition}{Proposition}[section]
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\newtheorem{example}{Example}[section]
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\newtheorem{problem}{Problem}[section]
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\newtheorem{definition}{Definition}[section]
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\newtheorem{theorem}{Theorem}[section]
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\newtheorem{lemma}[theorem]{Lemma}
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\newtheorem{corollary}[theorem]{Corollary}
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\newtheorem{proposition}[theorem]{Proposition}\newtheorem{example}[theorem]{Example}
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\newtheorem{problem}[theorem]{Problem}
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\newtheorem{definition}[theorem]{Definition}
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\newcommand{\contradiction}{%
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\ensuremath{{\Rightarrow\mspace{-2mu}\Leftarrow}}}
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