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| @ -1,63 +0,0 @@ | ||||
| % use [nosolutions] flag to hide solutions. | ||||
| % use [solutions] flag to show solutions. | ||||
| \documentclass[ | ||||
| 	solutions, | ||||
| 	singlenumbering | ||||
| ]{../../resources/ormc_handout} | ||||
|  | ||||
| % Set to true to show knot measurements. | ||||
| % Only used in tikzset.tex | ||||
| \newif{\ifDebugKnot} | ||||
| %\DebugKnottrue | ||||
| \DebugKnotfalse | ||||
| \input{tikzset.tex} | ||||
|  | ||||
|  | ||||
| % Problems from "Why knot" | ||||
| % | ||||
| % Create largest crossing number with cord | ||||
| % Human knot number: how many humans do you need to make the knot? | ||||
| % Human knot number for trefoil composition? | ||||
| %	(looks like a wrap around center string) | ||||
| % | ||||
| % Figure-8 knot: mirror without letting go | ||||
|  | ||||
| %\usepackage{lua-visual-debug} | ||||
|  | ||||
|  | ||||
| \begin{document} | ||||
| 	\maketitle | ||||
| 		<Advanced 2> | ||||
| 		<Spring 2023> | ||||
| 		{Knots and Braids} | ||||
| 		{ | ||||
| 			Prepared by Mark on \today | ||||
| 		} | ||||
|  | ||||
|  | ||||
| 	\input{parts/0 intro.tex} | ||||
| 	\input{parts/1 composition.tex} | ||||
| 	\input{parts/2 links.tex} | ||||
| 	\input{parts/3 sticks.tex} | ||||
| 	\input{parts/4 braids.tex} | ||||
|  | ||||
|  | ||||
| 	% Make sure the knot table is on an odd page | ||||
| 	% so it may be removed in a double-sided | ||||
| 	% handout. | ||||
| 	\checkoddpage | ||||
| 	\ifoddpage\else | ||||
| 		\vspace*{\fill} | ||||
| 		\begin{center} | ||||
| 		{ | ||||
| 			\Large | ||||
| 			\textbf{This page isn't empty.} | ||||
| 		} | ||||
| 		\end{center} | ||||
| 		\vspace{\fill} | ||||
| 		\pagebreak | ||||
| 	\fi | ||||
|  | ||||
| 	\input{parts/table} | ||||
|  | ||||
| \end{document} | ||||
| @ -1,159 +0,0 @@ | ||||
| \section{Introduction} | ||||
|  | ||||
| \definition{} | ||||
| To form a \textit{knot}, take a string, tie a knot, then join the ends. \par | ||||
| You can also think of a knot as a path in three-dimensional space that doesn't intersect itself: | ||||
|  | ||||
| \vspace{2mm} | ||||
|  | ||||
| \begin{center} | ||||
| 	\begin{minipage}[t]{0.3\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture}[scale = 0.8, baseline=(p)] | ||||
| 		\begin{knot} | ||||
| 			\strand | ||||
| 				(1,2) .. controls +(-45:1) and +(1,0) .. | ||||
| 				(0, 0) .. controls +(-1,0) and +(-90 -45:1) .. | ||||
| 				(-1,2); | ||||
| 		\end{knot} | ||||
|  | ||||
| 		\coordinate (p) at (current bounding box.center); | ||||
| 		\end{tikzpicture} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.3\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture}[scale = 0.8, baseline=(p)] | ||||
|  | ||||
| 		% Knot is stupid and includes invisible handles in the tikz bounding box. This line crops the image to fix that. | ||||
| 		\clip (-2,-1.7) rectangle + (4, 4); | ||||
|  | ||||
| 		\begin{knot}[ | ||||
| 			consider self intersections=true, | ||||
| 			flip crossing = 2, | ||||
| 		] | ||||
| 			\strand | ||||
| 				(1,2) .. controls +(-45:1) and +(120:-2.2) .. | ||||
| 				(210:2) .. controls +(120:2.2) and +(60:2.2) .. | ||||
| 				(-30:2) .. controls +(60:-2.2) and +(-90 -45:1) .. | ||||
| 				(-1,2); | ||||
| 		\end{knot} | ||||
|  | ||||
| 		\coordinate (p) at (current bounding box.center); | ||||
|  | ||||
|  | ||||
| 		\end{tikzpicture} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.3\textwidth} | ||||
| 		\begin{center} | ||||
| 			\begin{tikzpicture}[scale = 0.8, baseline=(p)] | ||||
|  | ||||
| 			\clip (-2,-1.7) rectangle + (4, 4); | ||||
|  | ||||
|  | ||||
| 			\begin{knot}[ | ||||
| 				consider self intersections=true, | ||||
| 				flip crossing = 2, | ||||
| 			] | ||||
| 				\strand | ||||
| 					(0,2) .. controls +(2.2,0) and +(120:-2.2) .. | ||||
| 					(210:2) .. controls +(120:2.2) and +(60:2.2) .. | ||||
| 					(-30:2) .. controls +(60:-2.2) and +(-2.2,0) .. | ||||
| 					(0,2); | ||||
| 			\end{knot} | ||||
|  | ||||
| 			\coordinate (p) at (current bounding box.center); | ||||
|  | ||||
| 			\end{tikzpicture} | ||||
| 		\end{center} | ||||
| 		\end{minipage} | ||||
| \end{center} | ||||
|  | ||||
| If two knots may be deformed into each other without cutting, we say they are \textit{isomorphic}. \par | ||||
| If two knots are isomorphic, they are essentially the same knot. | ||||
|  | ||||
| \definition{} | ||||
| The simplest knot is the \textit{unknot}. It is show below on the left. \par | ||||
| The simplest nontrivial knot is the \textit{trefoil} knot, shown to the right. | ||||
|  | ||||
| \begin{center} | ||||
| 	\begin{minipage}[t]{0.48\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture}[baseline=(p)] | ||||
|  | ||||
| 		\draw[circle] (0,0) circle (1); | ||||
|  | ||||
| 		\coordinate (p) at (current bounding box.center); | ||||
| 		\end{tikzpicture} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.48\textwidth} | ||||
| 	\begin{center} | ||||
| 	\begin{tikzpicture}[baseline=(p), scale = 0.8] | ||||
| 		\clip (-2,-1.7) rectangle + (4, 4); | ||||
|  | ||||
| 		\begin{knot}[ | ||||
| 			consider self intersections=true, | ||||
| 			flip crossing = 2, | ||||
| 		] | ||||
| 			\strand | ||||
| 				(0,2) .. controls +(2.2,0) and +(120:-2.2) .. | ||||
| 				(210:2) .. controls +(120:2.2) and +(60:2.2) .. | ||||
| 				(-30:2) .. controls +(60:-2.2) and +(-2.2,0) .. | ||||
| 				(0,2); | ||||
| 		\end{knot} | ||||
| 		\coordinate (p) at (current bounding box.center); | ||||
|  | ||||
| 		\end{tikzpicture} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| \end{center} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \problem{} | ||||
| Below are the only four knots with one crossing. \par | ||||
| Show that every nontrivial knot more than two crossings. \par | ||||
| \hint{There are four knots with two crossings. What are they?} | ||||
|  | ||||
| \begin{center} | ||||
| 	\includegraphics[width=0.8\linewidth]{images/one crossing.png} | ||||
| \end{center} | ||||
|  | ||||
| \begin{solution} | ||||
| 	Draw them all. Each is isomorphic to the unknot. | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Show that this is the unknot. \par | ||||
| A wire or an extension cord may help. | ||||
|  | ||||
| \begin{center} | ||||
| 	\includegraphics[width=0.35\linewidth]{images/big unknot.png} | ||||
| \end{center} | ||||
|  | ||||
|  | ||||
| \definition{} | ||||
| As we said before, there are many ways to draw the same knot. \par | ||||
| We call each drawing a \textit{projection}. Below are four projections of the \textit{figure-eight knot}. | ||||
|  | ||||
|  | ||||
| \vspace{2mm} | ||||
| \begin{center} | ||||
| 	\includegraphics[width=0.8\linewidth]{images/figure eight many.png} | ||||
| \end{center} | ||||
| \vspace{2mm} | ||||
|  | ||||
| \problem{} | ||||
| Convince yourself that these are equivalent. \par | ||||
| Try to deform them into each other with a cord! | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,135 +0,0 @@ | ||||
| \section{Knot Composition} | ||||
|  | ||||
| Say we have two knots $A$ and $B$. | ||||
| The knot $A \boxplus B$ is created by cutting $A$ and $B$ and joining their ends: | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.15\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/figure eight.png} | ||||
| 		$A$ | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.13\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/trefoil.png} | ||||
| 		$B$ | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.3\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/composition a.png} | ||||
| 		$A \boxplus B$ | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill~ | ||||
| \end{center} | ||||
|  | ||||
| We must be careful to avoid new crossings when composing knots: | ||||
|  | ||||
| \vspace{2mm} | ||||
| \begin{center} | ||||
| 	\includegraphics[width=0.45\linewidth]{images/composition b.png} | ||||
| \end{center} | ||||
| \vspace{2mm} | ||||
|  | ||||
| We say a knot is \textit{composite} if it can be obtained by composing two other knots. \par | ||||
| We say a knot is \textit{prime} otherwise. | ||||
|  | ||||
| \problem{} | ||||
| For any knot $K$, what is $K \boxplus \text{unknot}$? | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Use a pencil or a cord to compose the figure-eight knot with itself. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \vfill | ||||
| \pagebreak{} | ||||
|  | ||||
| \problem{} | ||||
| The following knots are composite. \par | ||||
| What are their prime components? \par | ||||
| Try to make them with a cord. \par | ||||
| \hint{Use the table at the back of this handout to decompose the second knot.} | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\includegraphics[height=30mm]{images/decompose a.png} | ||||
| 	\hfill | ||||
| 	\includegraphics[height=30mm]{images/decompose b.png} | ||||
| 	\hfill~\par | ||||
| 	\vspace{4mm} | ||||
| \end{center} | ||||
|  | ||||
| \begin{solution} | ||||
| 	The first is easy, it's the trefoil composed with itself. \par | ||||
|  | ||||
| 	\vspace{2mm} | ||||
|  | ||||
| 	The second is knot $5_2$ composed with itself. \par | ||||
| 	Note that the \say{three-crossing figure eight} is another projection of $5_2$. \par | ||||
| 	The figure-eight knot is NOT a part of this composition. Look closely at its crossings. | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
|  | ||||
| \definition{} | ||||
| When we compose two knots, we may get different results. To fully understand this fact, we need to define knot \textit{orientation}. | ||||
|  | ||||
| \vspace{2mm} | ||||
|  | ||||
| An \textit{oriented knot} is created by defining a \say{direction of travel.} \par | ||||
| There are two distinct ways to compose a pair of oriented knots: | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.25\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/orientation b.png} | ||||
| 		Matching orientation | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.25\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/orientation c.png} | ||||
| 		Inverse orientation | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill~ | ||||
| \end{center} | ||||
|  | ||||
| In this example, both compositions happen to give the same result. This is because the trefoil knot is \textit{invertible}: its direction can be reversed by deforming it. This is not true in general, as you will soon see. | ||||
|  | ||||
| \problem{} | ||||
| Invert a directed trefoil. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| The smallest non-invertible knot is $8_{17}$, shown below. \par | ||||
| Compose $8_{17}$ with itself to obtain two different knots. | ||||
|  | ||||
| \begin{center} | ||||
| 	\includegraphics[height=30mm]{knot table/8_17.png} \par | ||||
| 	\vspace{2mm} | ||||
| 	{\large Knot $8_{17}$} | ||||
| \end{center} | ||||
|  | ||||
| \begin{solution} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=0.8\linewidth]{images/noninvertible.png} | ||||
| 	\end{center} | ||||
| \end{solution} | ||||
|  | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,77 +0,0 @@ | ||||
| \section{Links} | ||||
|  | ||||
| \definition{} | ||||
| A \textit{link} is a set of knots intertwined with each other. \par | ||||
| Just as with knots, we say that two links are \textit{isomorphic} if one can be deformed into the other. | ||||
|  | ||||
| \vspace{2mm} | ||||
|  | ||||
| The \textit{Whitehead link} is one of the simplest links we can produce. \par | ||||
| It consists of two knots, so we say it is a \textit{link of two components}. | ||||
| Two projections of the Whitehead link are shown below. | ||||
|  | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.27\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/whitehead a.png} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.25\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/whitehead b.png} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill~ | ||||
| \end{center} | ||||
|  | ||||
|  | ||||
| \definition{} | ||||
| The \textit{$n$-unlink} is the link that consists of $n$ disjoint unknots. \par | ||||
| The 3-unlink is shown below: | ||||
|  | ||||
| \begin{center} | ||||
| 	\begin{tikzpicture} | ||||
|  | ||||
| 	\draw[circle] (0,0) circle (0.7); | ||||
| 	\draw[circle] (2,0) circle (0.7); | ||||
| 	\draw[circle] (4,0) circle (0.7); | ||||
|  | ||||
| 	\end{tikzpicture} | ||||
| \end{center} | ||||
|  | ||||
| \definition{} | ||||
| We say a nontrivial link is \textit{Brunnian} if we get an $n$-unlink after removing any component. | ||||
|  | ||||
| \vspace{2mm} | ||||
|  | ||||
| The \textit{Borromean Rings} are a common example of this. If we were to cut any of the three rings, the other two would fall apart. | ||||
|  | ||||
| \begin{center} | ||||
| 	\includegraphics[height=3cm]{images/borromean.png} | ||||
| \end{center} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
|  | ||||
| \problem{} | ||||
| Find a Brunnian link with four components. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Find a Brunnian link with $n$ components. | ||||
|  | ||||
| \begin{solution} | ||||
| 	One of many possible solutions: | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=40mm]{images/brunnian.png} | ||||
| 	\end{center} | ||||
| \end{solution} | ||||
|  | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,62 +0,0 @@ | ||||
| \section{Knots and Sticks} | ||||
|  | ||||
| \definition{} | ||||
| The \textit{stick number} of a knot is the smallest number of \say{sticks} you must glue together to make the knot. An example of this is below. | ||||
|  | ||||
| \begin{center} | ||||
| 	\includegraphics[width=30mm]{images/sticks.png} | ||||
| \end{center} | ||||
|  | ||||
| \problem{} | ||||
| Make a trefoil knot with sticks. \par | ||||
| How many do you need? | ||||
|  | ||||
| \begin{solution} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=20mm]{images/stick trefoil.png} | ||||
| 	\end{center} | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| How many sticks do you need to make a figure-eight knot? | ||||
|  | ||||
| \begin{solution} | ||||
| 	The figure-eight knot has stick number 7. \par | ||||
| 	In fact, it is the only knot with stick number 7. | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \problem{} | ||||
| Make the knot $5_1$ (refer to the knot table) with eight sticks. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Show that the only nontrivial knot you can make with six sticks is the trefoil. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Let $S(k)$ be the stick number of a knot $k$. \par | ||||
| Show that $S(j \boxplus k) \leq s(j) + s(k) - 1$ | ||||
|  | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| What is the stick number of $(\text{trefoil} \boxplus \text{trefoil})$? | ||||
|  | ||||
| \begin{solution} | ||||
| 	You can make $(\text{trefoil} \boxplus \text{trefoil})$ with 8 sticks. | ||||
|  | ||||
| 	\begin{center} | ||||
| 		\includegraphics[angle=90, width=40mm]{images/stick trefoil composition.png} | ||||
| 	\end{center} | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,204 +0,0 @@ | ||||
| \section{Braids} | ||||
|  | ||||
| \definition{} | ||||
| A \textit{braid} is a set of $n$ strings with fixed ends. Two braids are equivalent if they may be deformed into each other without disconnecting the strings. Two braids are shown below: | ||||
|  | ||||
| \begin{center} | ||||
| \begin{tikzpicture} | ||||
| 	\pic[rotate=90, name prefix=braid] { | ||||
| 		braid = {s_2^{-1} s_1^{-1} s_2 s_2 s_3^{-1} } | ||||
| 	}; | ||||
|  | ||||
| 	\braidbars{4} | ||||
| \end{tikzpicture} | ||||
| \hfill | ||||
| \begin{tikzpicture} | ||||
| 	\pic[rotate=90, name prefix=braid] { | ||||
| 		braid = {s_2^{-1} s_3 s_2 s_1 s_1^{-1} s_2^{-1} s_3^{-1} s_1^{-1} s_2 s_2 s_3^{-1} } | ||||
| 	}; | ||||
| 	\braidbars{4} | ||||
| \end{tikzpicture} | ||||
| \end{center} | ||||
|  | ||||
| \problem{} | ||||
| Convince yourself that the braids above are equivalent. | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \definition{} | ||||
| A braid can be \textit{closed} by conecting its ends: | ||||
|  | ||||
| \begin{center} | ||||
| \begin{tikzpicture} | ||||
| 	\pic[rotate=90, name prefix=braid] { | ||||
| 		braid = {s_2^{-1} s_1^{-1} s_2 s_2 s_3^{-1} } | ||||
| 	}; | ||||
|  | ||||
| 	\closebraid{4} | ||||
| 	\widebraidbars{4} | ||||
| \end{tikzpicture} | ||||
| \end{center} | ||||
|  | ||||
| \problem{} | ||||
| When will a closed braid form a knot? \par | ||||
| When will a closed braid form a link? | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Draw a braid that creates a $3$-unlink when closed. | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \problem{}<braidify> | ||||
| Draw the following knots as closed braids. | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.13\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/trefoil.png} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.15\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/closed braid a.png} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.15\textwidth} | ||||
| 	\begin{center} | ||||
| 		\includegraphics[width=\linewidth]{images/closed braid b.png} | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill~ | ||||
| \end{center} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \problem{} | ||||
| We can describe the projection of a braid by listing which strings cross over and under each other as we move along the braid. \par | ||||
|  | ||||
| \vspace{2mm} | ||||
|  | ||||
| For example, consider a three-string braid. If the first string crosses over the second, we'll call that a $1$ crossing. If first string crosses \textbf{under} the second, we'll call that a $-1$ crossing. | ||||
|  | ||||
| \begin{center} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.2\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture} | ||||
| 			\pic[ | ||||
| 				name prefix = braid, | ||||
| 				braid/number of strands = 3 | ||||
| 			] { | ||||
| 				braid = {s_1} | ||||
| 			}; | ||||
| 		\end{tikzpicture} \par | ||||
| 		\texttt{1} crossing | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.2\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture} | ||||
| 			\pic[ | ||||
| 				name prefix = braid, | ||||
| 				braid/number of strands = 3 | ||||
| 			] { | ||||
| 				braid = {s_1^{-1}} | ||||
| 			}; | ||||
| 		\end{tikzpicture} \par | ||||
| 		\texttt{-1} crossing | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.2\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture} | ||||
| 			\pic[ | ||||
| 				name prefix = braid, | ||||
| 				braid/number of strands = 3 | ||||
| 			] { | ||||
| 				braid = {s_2} | ||||
| 			}; | ||||
| 		\end{tikzpicture} \par | ||||
| 		\texttt{2} crossing | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill | ||||
| 	\begin{minipage}[t]{0.2\textwidth} | ||||
| 	\begin{center} | ||||
| 		\begin{tikzpicture} | ||||
| 			\pic[ | ||||
| 				name prefix = braid, | ||||
| 				braid/number of strands = 3 | ||||
| 			] { | ||||
| 				braid = {s_2^{-1}} | ||||
| 			}; | ||||
| 		\end{tikzpicture} \par | ||||
| 		\texttt{-2} crossing | ||||
| 	\end{center} | ||||
| 	\end{minipage} | ||||
| 	\hfill~ | ||||
| \end{center} | ||||
|  | ||||
| \problem{} | ||||
| Verify that the following is a $[1, 2, 1, -2, 1, 2]$ braid. \par | ||||
| Read the braid left to right, with the bottom string numbered $1$. | ||||
|  | ||||
| \begin{center} | ||||
| 	\begin{tikzpicture} | ||||
| 		\pic[ | ||||
| 			rotate = 90, | ||||
| 			name prefix = braid, | ||||
| 			braid/number of strands = 3 | ||||
| 		] { | ||||
| 			% When we rotate a braid | ||||
| 			braid = {s_1 s_2 s_1 s_2^{-1} s_1 s_2} | ||||
| 		}; | ||||
| 		\labelbraidstart{3} | ||||
| 	\end{tikzpicture} | ||||
| \end{center} | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Draw the five-string braid defined by $[1, 3, 4, -3, 2, 4]$ | ||||
|  | ||||
| \begin{solution} | ||||
| 	\begin{center} | ||||
| 	\begin{tikzpicture} | ||||
| 		\pic[ | ||||
| 			rotate = 90, | ||||
| 			name prefix = braid, | ||||
| 			braid/number of strands = 5 | ||||
| 		] { | ||||
| 			braid = {s_1 s_3 s_4 s_3^{-1} s_2 s_4} | ||||
| 		}; | ||||
|  | ||||
| 		\labelbraidstart{5} | ||||
| 		\labelbraidend{5} | ||||
| 	\end{tikzpicture} | ||||
| 	\end{center} | ||||
| \end{solution} | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
|  | ||||
| \problem{} | ||||
| Identify the knot generated by the 4-string braid $[(-1, 2, 3)^2,~(3)^3]$ \par | ||||
| \hint{$[(1, 2)^2, 3] = [1, 2, 1, 2, 3]$} | ||||
| \hint{This knot has 6 crossings. Use the knot table.} | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| \problem{} | ||||
| Show that the $n$-string braid $[(1, 2, ..., n-1)^m]$ forms a knot iff $m$ and $n$ are coprime. | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,42 +0,0 @@ | ||||
| \section{Table of Prime Knots} | ||||
| A knot's \textit{crossing number} is the minimal number of crossings its projection must contain. \par | ||||
| Finding a knot's crossing number is a fairly difficult problem. | ||||
|  | ||||
| \vspace{1mm} | ||||
|  | ||||
| This table contains the a 20 smallest prime knots, ordered by crossing number. \par | ||||
| Mirror images are not included, even if the mirror image produces a nonisomorphic knot. | ||||
|  | ||||
| \vfill | ||||
|  | ||||
| % Images are from the appendix of the Knot book. | ||||
| { | ||||
| 	\def\w{24mm} | ||||
| 	\newcounter{knotcounter} | ||||
|  | ||||
| 	\foreach \a in {% | ||||
| 		{3_1},{4_1},{5_1},{5_2},% | ||||
| 		{6_1},{6_2},{6_3},{7_1},% | ||||
| 		{7_2},{7_3},{7_4},{7_5},% | ||||
| 		{7_6},{7_7},{8_1},{8_2},% | ||||
| 		{8_3},{8_4},{8_5},{8_6}% | ||||
| 	}{ | ||||
| 		\stepcounter{knotcounter} | ||||
| 		\hfill | ||||
| 		\begin{minipage}{\w} | ||||
| 		\begin{center} | ||||
| 			\includegraphics[width=\linewidth]{knot table/\a.png} \par | ||||
| 			\vspace{2mm} | ||||
| 			{\huge $\a$} | ||||
| 		\end{center} | ||||
| 		\end{minipage} | ||||
| 		\ifnum\value{knotcounter}=4 | ||||
| 			\hfill~\par | ||||
| 			\vspace{4mm} | ||||
| 			\setcounter{knotcounter}{0} | ||||
| 		\fi | ||||
| 	} | ||||
| } | ||||
|  | ||||
| \vfill | ||||
| \pagebreak | ||||
| @ -1,106 +0,0 @@ | ||||
| \usetikzlibrary{ | ||||
| 	knots, | ||||
| 	hobby, | ||||
| 	braids, | ||||
| 	decorations.pathreplacing, | ||||
| 	shapes.geometric, | ||||
| 	calc | ||||
| } | ||||
|  | ||||
| \ifDebugKnot | ||||
| 	\tikzset{ | ||||
| 		knot diagram/draft mode = crossings, | ||||
| 		knot diagram/only when rendering/.style = { | ||||
| 			show curve endpoints, | ||||
| 			%show curve controls | ||||
| 		} | ||||
| 	} | ||||
| \fi | ||||
|  | ||||
| \tikzset{ | ||||
| 	circle/.style = { | ||||
| 		line width = 0.8mm, | ||||
| 	}, | ||||
| 	knot diagram/every strand/.append style={ | ||||
| 		line width = 0.8mm, | ||||
| 		black | ||||
| 	}, | ||||
| 	show curve controls/.style={ | ||||
| 		postaction=decorate, | ||||
| 		decoration={ | ||||
| 			show path construction, | ||||
| 			curveto code={ | ||||
| 				\draw[blue, dashed] | ||||
| 					(\tikzinputsegmentfirst) -- (\tikzinputsegmentsupporta) | ||||
| 					node [at end, draw, solid, red, inner sep=2pt]{} | ||||
| 				; | ||||
|  | ||||
| 				\draw[blue, dashed] | ||||
| 					(\tikzinputsegmentsupportb) -- (\tikzinputsegmentlast) | ||||
| 					node [at start, draw, solid, red, inner sep=2pt]{} | ||||
| 					node [at end, fill, red, ellipse, inner sep=2pt]{} | ||||
| 				; | ||||
| 			} | ||||
| 		} | ||||
| 	}, | ||||
| 	show curve endpoints/.style={ | ||||
| 		postaction=decorate, | ||||
| 		decoration={ | ||||
| 			show path construction, | ||||
| 			curveto code={ | ||||
| 				\node [fill, blue, ellipse, inner sep=2pt] at (\tikzinputsegmentlast) {}; | ||||
| 			} | ||||
| 		} | ||||
| 	}, | ||||
| 	braid/gap = 0.2, | ||||
| 	braid/width = 5mm, | ||||
| 	braid/height = -8mm, | ||||
| 	braid/control factor = 0.75, | ||||
| 	braid/nudge factor = 0.05, | ||||
| 	braid/every strand/.style = { | ||||
| 		line width = 0.7mm | ||||
| 	}, | ||||
| 	bar/.style = { | ||||
| 		% Should match braid line width | ||||
| 		line width = 0.7mm, | ||||
| 		fill = black | ||||
| 	} | ||||
| } | ||||
|  | ||||
| % Braid bar macro | ||||
| % Argument: number of strands | ||||
| \newcommand{\braidbars}[1]{ | ||||
| 	\draw[bar] ([xshift=-0.7mm]braid-1-s) rectangle (braid-#1-s); | ||||
| 	\draw[bar] ([xshift=-0.7mm]braid-rev-1-e) rectangle (braid-rev-#1-e); | ||||
| } | ||||
| \newcommand{\widebraidbars}[1]{ | ||||
| 	\draw[bar] ([xshift=-0.7mm,yshift=-2mm]braid-1-s) rectangle ([yshift=2mm]braid-#1-s); | ||||
| 	\draw[bar] ([xshift=-0.7mm,yshift=-2mm]braid-rev-1-e) rectangle ([yshift=2mm]braid-rev-#1-e); | ||||
| } | ||||
|  | ||||
| % Closed braid loops | ||||
| % Argument: number of strands | ||||
| \newcommand{\closebraid}[1]{ | ||||
| 	\foreach \x in {1, ..., #1} { | ||||
| 		\draw[braid/every strand, rounded corners = 4mm] | ||||
| 			(braid-\x-s) -- | ||||
| 			([shift=(west:5*\x mm)]braid-\x-s) -- | ||||
| 			([shift=(west:5*\x mm),shift=(south:10*\x mm)]braid-\x-s) -- | ||||
| 			([shift=(east:5*\x mm),shift=(south:10*\x mm)]braid-rev-\x-e) -- | ||||
| 			([shift=(east:5*\x mm)]braid-rev-\x-e) -- | ||||
| 			(braid-rev-\x-e) | ||||
| 		; | ||||
| 	} | ||||
| } | ||||
|  | ||||
| \newcommand{\labelbraidstart}[1]{ | ||||
| 	\foreach \x in {1, ..., #1} { | ||||
| 		\node at ([xshift=-2mm]braid-\x-s) {$\x$}; | ||||
| 	} | ||||
| } | ||||
|  | ||||
| \newcommand{\labelbraidend}[1]{ | ||||
| 	\foreach \x in {1, ..., #1} { | ||||
| 		\node at ([xshift=2mm]braid-\x-e) {$\x$}; | ||||
| 	} | ||||
| } | ||||