\documentclass{article}
\usepackage[all,knot,poly]{xy}
\begin{document}
\[
\xy
(-40,0)*{\sigma^{-1} _i \sigma _i:}
\vtwist~{(-3,6)}{(3,6)}{(-3,0)}{(3,0)};
\vtwist~{(3,0)}{(-3,0)}{(3,-6)}{(-3,-6)};
(-12,9)*{1};(12,9)*{n};(-3,9)*{i};(3,9)*{i+1};
(-12,-6)*{}; (-12,6)*{} **\dir{-};
(12,-6)*{}; (12,6)*{} **\dir{-};
(-7,0)*{\dots}; (7,0)*{\dots};
\endxy
\]

{\tiny
\[
\xy
%(-40,0)*{\sigma:}
(-9,9)*{1};(9,9)*{4};(-3,9)*{2};(3,9)*{3};
(-3,-6)*{}; (-3,6)*{} **\dir{-};
(3,-6)*{}; (3,6)*{} **\dir{-};
(-9,-6)*{}; (-9,6)*{} **\dir{-};
(9,-6)*{}; (9,6)*{} **\dir{-};
\endxy
\]
}
\end{document}