I tried to use \align
in Texmacs. But the line breaking of the exported Latex code is not correct. The \eqnarray
family has no such problem. Let me explain these in details.

First, the identation of Texmacs by default is off. In order to see the visual, go to menu
Document
>Paragraph
>Basic
>First Identation
, and select1tab
. 
See the picture. Note that the
displayed math formula
is in thealign
enviroment

The above exported to Latex:
\begin{document}
Let $a = 1$, $b = 2$ and
\begin{align}
c & = a + b.
\end{align}
\
Therefore $c = 3$. Let
\begin{align}
d & = 2 a + b,
\end{align}
then $d = 4$.
 Compiled to
pdf
, this code generates
Note that all lines are indented with extra one line break before “Therefore” and extra line breaks after and
, let
.
 The Correct Latex Code should be
\begin{document}
Let $a = 1$, $b = 2$ and
\begin{align}
c & = a + b.
\end{align}
Therefore $c = 3$. Let
\begin{align}
d & = 2 a + b,
\end{align}
then $d = 4$.