add frieze patterns placeholder in geometry chapter

geometry.tex

@@ -366,6 +366,75 @@ \section{The icosahedron}
 \end{sidecaption}
 \end{figure}
 
+\section{Frieze patterns}
+
+\begin{center}
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,1,...,8} {
+      \draw (\i,.5) -- (.5+\i,0);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,2,...,8} {
+      \draw (\i,.5) -- (.5+\i,0);
+    }
+    \foreach \i in {1,3,...,7} {
+      \draw (\i,-.5) -- (.5+\i,0);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,1,...,8} {
+      \draw (\i,.5) -- (\i,0);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,1,...,8} {
+      \draw (\i,.5) -- (1+\i,-.5);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,2,...,8} {
+      \draw (\i,.5) -- (1+\i,-.5);
+    }
+    \foreach \i in {1,3,...,7} {
+      \draw (\i,-.5) -- (1+\i,.5);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,1,...,8} {
+      \draw (\i,.5) -- (.5+\i,0);
+      \draw (\i,-.5) -- (.5+\i,0);
+    }
+  \end{tikzpicture}\\[10pt]
+  \begin{tikzpicture}[thick]
+    \draw[dashed,thin] (0.25,-1) rectangle (8.25,1);
+    \clip (0.25,-1) rectangle (8.25,1);
+    \draw (-1,0) -- (9,0);
+    \foreach \i in {0,1,...,8} {
+      \draw (\i,.5) -- (\i,-.5);
+    }
+  \end{tikzpicture}
+
+\end{center}
+
 \section{Incidence geometries and the Levi graph}
 
 \section{Affine geometry}
@@ -390,6 +459,7 @@ \subsection{the projective group and projectivities}
 \subsection{projective properties (cross-ratio)}
 \subsection{fundamental theorem of projective geometry}
 
+
 % Local Variables:
 % fill-column: 144
 % latex-block-names: ("lemma" "theorem" "remark" "definition" "corollary" "fact" "properties" "conjecture" "proof" "question" "proposition" "exercise")