# 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 '14 at 11:26
@JosephWright Tested it; is correct. – JPi Aug 10 '14 at 11:41

The documentation for mtpro2 makes it clear that \PARENS is a command taking one argument
\PARENS{\frac{x}{y}}

It's unsurprising that if you use it as an environment odd things happen (here, it grabs \frac but not the arguments to \frac, then problems arise as \frac looks for two arguments and fails to find them).
@mert You could define a command which uses the environ package to collect up the content of the environment then use it as the argument to \PAREN. I think that would be a separate question :-) – Joseph Wright Aug 10 '14 at 11:59