# How can I cancel the effect of {} in untouchable macros?

Assuming that we cannot change the implementation of \blackbox that is

\def\blackbox#1{{}#1}


What should we pass to \blackbox such that $\blackbox{<something we need to pass>}$ produces the same result as $-y$? In other words, how can I cancel the effect of {} defined in \blackbox?

\documentclass[preview,border=12pt,12pt,varwidth]{standalone}
\usepackage{amsmath}

\def\blackbox#1{{}#1}

\begin{document}
\noindent\huge
$-y$\\ % output that I want to achieve
$\blackbox{-y}$ % how can I remove the effect of {} in \blackbox?
\end{document}


## Real scenario

I want use \equ for representing $-3y=59$ but if I use \equ{}{-3y}{59} the output is not identical because of the prefix {} defined in \equ.

\documentclass[preview,border=12pt,12pt]{standalone}
\usepackage{mathtools,booktabs}

\newcommand\specifier{%
r@{}r@{}l
r@{}r@{}l
@{}c}

\newcommand\ope[1]{~\smash{\raisebox{.8\normalbaselineskip}{$#1$}}}
\newcommand\equ[3]{{}#1 & {}#2 & {}=#3}

\begin{document}
$\begin{array}{\specifier} \equ{3x}{+3y}{7} & \act{1} & \equ{3x}{+3y}{7} \\[\jot] \equ{3x}{}{22} & \act{3} & \equ{3x}{}{66} & \ope{-} \\\cmidrule{5-7} && & & \equ{}{-3y}{59} \\[\jot] && & & \equ{}{y}{-59/3} \\ \end{array}$
\end{document}


-

Build a math atom:

$\blackbox{{-y}}$

-

Another possibility:

\def\gobble#1{}
$\expandafter\gobble\blackbox{-y}$

-
+1 Thanks for adding more extra keystrokes. –  stalking isn't tolerated May 19 '14 at 7:21
@MoneyOrientedProgrammer This answer does in fact more closely answer your question (as stated in the title) although Herbert's answer is better for the particular application. –  David Carlisle May 19 '14 at 13:06