[Tex/LaTex] Difference between \big[ and \bigl[

Question

What is the difference between \big[ (or equivalently \big() and \bigl[? Is it always necessary to mention l (left) and r (right)?

Answer 1

\bigl declares an opening math delimiter with less horizontal spacing than the unspecified \big. \bigr defines a closing math delimiter. Using a \bigl and \bigr pair you could get the brackets or parentheses closer to the term within.

Just compare:

\documentclass{article}
\begin{document}
$\bigl[ \times \bigr]$

$\big[ \times \big]$
\end{document}

Output:

The definitions in latex.ltx are:

\def\bigl{\mathopen\big}
\def\bigm{\mathrel\big}
\def\bigr{\mathclose\big}