Set qed-symbol aligned with an enumerate/align environment

Question

When my proof end with an enumeration resp. a formula, the qed-symbol is set in a new line. But I want it to be in the last line of the enumeration resp. the formula.

Here is what is looks like:

Here is my code:

\documentclass[ngerman, fontsize=11pt, DIV=15, ,BCOR = 10mm, parskip=half-, twoside]{scrbook}
\usepackage{amsmath, amsthm}
\usepackage{cleveref}
\begin{document}
\begin{proof}
    We want to prove
\begin{enumerate}
    \item that this is true
    \item and that the QED-symbol is not on this line. But it is not, and that makes me sad.
\end{enumerate}
\end{proof}

%
    \begin{proof}
    We want to prove that
    \begin{align}
        1+2 = 4
    \end{align}
\end{proof}
\end{document}

Answer 1

You use \qedhere.

\documentclass{article}
\usepackage{amsmath, amsthm}
\begin{document}
\begin{proof}
We want to prove
\begin{enumerate}
  \item that this is true
  \item and that the QED-symbol is not on this line.
        But it is not, and that makes me sad.\qedhere
\end{enumerate}
\end{proof}
\begin{proof}
We want to prove that
\begin{equation}
  1+2 = 4 \qedhere
\end{equation}
\end{proof}
\begin{proof}
We want to prove that
\begin{align}
  1+2 &= 3+5 \
      &= 4 \qedhere
\end{align}
\end{proof}
\end{document}

Note that for single equation align should not be used.