Here it is. I am learning newenvironment
\documentclass[12pt]{book}%
\usepackage{amsmath}
\usepackage{longtable}
\usepackage{listings}

\newenvironment{CODE}{\begin{lstlisting}}{\end{lstlisting}\ignorespacesafterend}

\begin{document}
\begin{CODE}
x
\end{CODE}
\end{document}

\documentclass[12pt]{book}%
\usepackage{amsmath}
\usepackage{breqn}
\newenvironment{myequation}
{\begin{dmath*}}{\end{dmath*}\ignorespacesafterend}

\begin{document}
\begin{myequation}%
x
\end{myequation}
\end{document}

\documentclass[12pt]{book}%
\usepackage{amsmath}

\newenvironment{myequation}
{\begin{align}}{\end{align}\ignorespacesafterend}

\begin{document}
\begin{myequation}%
x
\end{myequation}
\end{document}

\documentclass{article}

\usepackage{amsmath}

\usepackage{showframe}

\begin{document}

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam fringilla dictum metus. Donec euismod diam eget augue tempus, vel facilisis eros maximus:
\begin{align*}
  A &= B,
  \intertext{
therefore
  }
  C &= DEF,
\end{align*}
quod erat demonstrandum.

\end{document}

\RequirePackage{tabu}
\show\tabulinesep

> \tabulinesep=macro:
->\edef \tabu@C@linesep {\the \numexpr \tabu@C@linesep +1}\iftabu@everyrow \aft
ergroup \tabu@Glinesep \else \aftergroup \tabu@n@Glinesep \fi \@ifnextchar ={\t
abu@gobbletoken \tabu@linesep } \tabu@linesep .

> nslookup ctan.org

Non-authoritative answer:
Name:	ctan.org
Address: 176.28.54.184

> nslookup mirror.ctan.org

Non-authoritative answer:
mirror.ctan.org	canonical name = comedy.dante.de.
Name:	comedy.dante.de
Address: 176.28.54.184

$ svn commit -m 'ignorespaces at start of \intertext' amsmath.dtx changes.txt README.txt
Sending        README.txt
Sending        amsmath.dtx
Sending        changes.txt
Transmitting file data ...done
Committing transaction...
Committed revision 1179.

I was trying to make my own command, only to find it is in the bookclass!
\documentclass[12pt]{book}%
\newcommand{\endTable}[0]
{
\end{longtable}
}
\begin{document}
test
\end{document}

Command \endTable already defined. }

How does one find out what `\endTable` do in book class? I had no idea the book class will export it own internal commands. Unless this is a command I can use? But what does it do? I googled it, and do not see how to learn about it.

@egreg Ok, I tried it. it works with longtable, and it is looks better. Here it is

\newenvironment{tbl}[3]
{
  \begin{longtable}[t]{|#3{#1\textwidth-2\tabcolsep-.6pt}
                       |#3{#2\textwidth-2\tabcolsep-.6pt}|
                      }\hline\endfirsthead
}
{
 \end{longtable}\ignorespacesafterend
}

And call it as
\begin{tbl}{0.45}{0.55}{p}
..
\end{tbl}

Thanks for the suggestion.

! LaTeX Error: Command \endTable already defined.
               Or name \end... illegal, see p.192 of the manual.