# mtpro2: PARENS environment error

\documentclass[10pt,a4paper]{book}
\usepackage[utf8x]{inputenc}
\usepackage{ucs}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage[lite]{mtpro2}

\begin{document}
$\begin{PARENS} \frac{x}{y} \end{PARENS}$
\end{document}

The code above gives the error

Argument of \frac has an extra }. \frac.

But if i write the \frac{x}{y} command in {} then there is no error.

I just want to learn how i can fix it?

-
According to pctex.com/files/managed/1/1b/mtpro2Abbrev.pdf, \PARENS is a command expecting an argument, so \PARENS{\frac{x}{y}} should be correct. Can you test? (I don't have mtpro2 installed.) –  Joseph Wright Aug 10 at 11:26
@JosephWright Tested it; is correct. –  JPi Aug 10 at 11:41