\psset{arrows=->,labelsep=3pt, linecolor=gray,mnode=circle,shortput=nab} \begin{psmatrix}[rowsep=20pt,colsep=28pt] A & B \\ $\sqrt{\frac{x + y}{z}}$ & D \psset{linestyle=dotted} \ncline{1,1}{1,2}^{\emph{firstly}} \ncline{1,2}{2,2}>{\emph{next}} \ncline{2,2}{2,1}_{\emph{then}} \ncline{2,1}{1,1}<{\emph{lastly}} \end{psmatrix}