\documentclass{amsart}
\usepackage{amsmath}

\DeclareMathOperator{\GL}{GL}
\newcommand{\SL}{\operatorname{SL}}

\numberwithin{equation}{section}

\subjclass[2010]{Primary: 11F67}

\begin{document}

\begin{align}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
  \tag{mylabel}
\end{align}

\begin{equation}
  \sum_{\begin{subarray}{l}i\in\Lambda\\ 0<j<n\end{subarray}} P(i,j)
\end{equation}

\begin{alignat}{3}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
  \tag*{mylabel}
\end{alignat}

\begin{alignat*}{3}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
\end{alignat*}

\begin{xalignat}{3}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
\end{xalignat}

\begin{xalignat*}{3}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
\end{xalignat*}

\begin{xxalignat}{3}
  f(x) &= \bigg\lvert 0 \bigg\rvert \\
  f(x) &= \Bigg\lVert 0 \Bigg\rVert
\end{xxalignat}

\end{document}