QED symbol on the same page as proof

Question

I'm using the proof environment from the amsthm package. In some cases, the last line of a proof falls at the end of a page, but the QED symbol (the little white box) ends up on the following page.

Is there any way to guarantee that in each instance of \begin{proof} ... \end{proof} in my document, the QED symbol will always be on the same page as the last line of the proof?

Here is an MWE which demonstrates this problem:

\documentclass{article}

\usepackage{lipsum}
\usepackage{amsthm}

\begin{document}

\begin{proof}

\lipsum[1-5]
This is the concluding line of the proof.

\end{proof}

This line is on the second page, below the QED symbol.

\end{document}

Answer 1

If you remove the blank line between This is the concluding line of the proof. and the \end{proof}, the problem disappears.

Answer 2

it's probable that your proof ends with a list or a display environment. since you're using amsthm, you can put \qedhere just before the end of that environment and the "tombstone" will be moved up onto the last line of the list or display.

edit: with the addition of a (non)working example, it became obvious that the problem was caused by a blank line before \end{proof}. never leave a blank line before \end{proof}; doing so will always result in the qed box being on a separate line, and even possibly on the next page as in this example.