\documentclass{article}
\newcommand{\Lbrack}[2]{#1\brack #2}
\newcommand{\Lbrace}[2]{#1\brace #2}
\begin{document}\noindent
The bracket structures in text formulas:
$\Lbrack{n+1}{m-1}$,
$\Lbrace{n+1}{m-1}$

\noindent The bracket struktures in displayed formulls:
\[ \Lbrack{n+1}{m} \] 
\[ \Lbrace{n+1}{m-1} \]
\end{document}
