# Spacing issue for newenvironment wrapper of equation environment

If I create a custom environment based on the equation environment, I get a spacing issue: the next line of text after my environment closes doesn't start on the left margin.

Example code:

\documentclass{article}
\begin{document}
\newenvironment{myenv$$}{$$$$}{$$}
\noindent $| \leftarrow$ this is the left margin.
\begin{myenv}
e ^{i \pi} + 1 = 0
\end{myenv}
$| \leftarrow$ this isn't the left margin.
\end{document}


Output:

Removing the newline after \end{myenv} solves the spacing problem, but the resulting code is not readable.

Of course, in this example I could just use the equation environment itself. My real issue involves a more complex custom environment that suffers from the same problem, and which also includes an equation environment within it.

-

The command terminates display math mode, so TeX resumes horizontal mode and only after this action it sees the end-of-line which follows \end{myenv}, processing it as part of the paragraph.
The solution is to append \ignorespacesafterend to the "end" part of the environment definition:
\newenvironment{myenv$$} {$$$$} {$$\ignorespacesafterend}