# Missing delimiter (. inserted) }

Here is the tex file which I encounter to this error, the result has no problem but the software show this error and I can't understand what is wrong (as the pdf result is ok!). So I will be glad if somone say me what is wrong or if there is nothing wrong say me how I can make the software to don't show it again.

\documentclass[10pt,a4paper]{book}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage[all]{xy}
\begin{document}
\xymatrix{
& X\ar[r]^f\ar@{}[dr]|(0.35){\big\circlearrowleft} & Y\\
\exists Z\subseteq X\;s.t. & Bl_Z(X)\ar[u]^{\pi}\ar@{.>}[ur]_{\exists f'} &
}
\end{document}


You used a \big command without adding a delimiter behind. Not sure what that was for, I suppose you were trying to get a larger \circlearrowleft? In that case, since you have loaded graphicx package already, you can try something like \scalebox{2}{$$\circlearrowleft$$}.