Como você pode deixar minhas duas flechas mais parecidas com as da foto.
\documentclass[10pt, border=.3cm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw (0,0)--(4,1)--(4,7)--(0,6)--(-4,7)--(-4,1)--cycle;
\draw(0,0)--(0,6);
\node (a) at (.715, 6.5) {};
\node (b) at (-.715, 6.5) {};
\draw[->] (a) to [out=120,in=60] (b);
\draw (9,7)--(13,7)--(12,3.5)--(13,0)--(9,0)--(8,3.5)--cycle;
\draw(12,3.5)--(8,3.5);
\draw(13,7)--(9.175,7.1)--(9.125,7.);
\draw(13,0)--(9.14,-.12)--(9.1,0);
\node (d) at (12.75, 3.8) {};
\node (c) at (12.5, 3.2) {};
\draw[->] (c) to [out=90,in=90] (d);
\end{tikzpicture}
\end{document}
Responder1
Coloque os pontos (c) e (d) com a mesma separação usada em (a) e (b). Use valores adequados para inpalavras out-chave e e controle a "arredondamento" da curva com a loosenesspalavra-chave:
\documentclass[10pt, border=.3cm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw (0,0)--(4,1)--(4,7)--(0,6)--(-4,7)--(-4,1)--cycle;
\draw(0,0)--(0,6);
\node (a) at (.715, 6.5) {};
\node (b) at (-.715, 6.5) {};
\draw[->] (a) to [out=90,in=90, looseness=2] (b);
\draw (9,7)--(13,7)--(12,3.5)--(13,0)--(9,0)--(8,3.5)--cycle;
\draw(12,3.5)--(8,3.5);
\draw(13,7)--(9.175,7.1)--(9.125,7.);
\draw(13,0)--(9.14,-.12)--(9.1,0);
\node (d) at (12.5, 3.5 + .715) {};
\node (c) at (12.5, 3.5 - .715) {};
\draw[->] (c) to [out=0,in=0,looseness=2] (d);
\end{tikzpicture}
\end{document}
Resultado:
