%Note: Add the -shell-escape flag to the compilation command to compile directly to an image.
%For .pdf files, use \documentclass[preview]{standalone}
%For .png files, (see http://tex.stackexchange.com/q/11866 for more info) use: \documentclass[convert={density=300,size=1080x800,outext=.png}]{standalone}
%For .svg files you need pdf2svg installed (see https://tex.stackexchange.com/a/51766/187911 for more info) use:
\documentclass[convert={outext=.svg,command=\unexpanded{pdf2svg \infile\space\outfile}},multi=false]{standalone}
\usepackage{tikz}
\usetikzlibrary{matrix,arrows,decorations.pathmorphing}
\usepackage[all]{xy}
\begin{document}
\begin{tikzpicture}[scale=2.5]
\node (MIOTAA) at (0,1) {$(s_1, \dots, s_a, s_{a+1} + s_{a+2})$};
\node (MIOTAB) at (3,1) {$(s_1, \dots, s_a, s_{a+1}, s_{a+2})$};
\node (NA) at (0,0) {$(s_1, \dots, s_a)$};
\node (NB) at (3,0) {$(s_1, \dots, s_a, s_{a+1})$};
\path[->,font=\scriptsize,>=angle 90]
(MIOTAB) edge node[above]{\scalebox{1.5}{$\mu_{\iota(a), \iota(a+1)}$}} (MIOTAA)
(MIOTAA) edge node[right]{\scalebox{1.5}{$F_{a}$}} (NA)
(MIOTAB) edge node[right]{\scalebox{1.5}{$F_{a+1}$}} (NB)
(NB) edge node[above]{\scalebox{1.5}{$\textrm{Pr}_{a,a+1}$}} (NA);
\end{tikzpicture}
\end{document}