Automatic linebreaking inside displaymath

Question

Yes, I know of the existence of breqn, and I am very excited about this package.

I am trying to write a mathematics paper, that will be typeset in two different styles (different page sizes, and different textblocks, &c).

At some point I have to typeset a long exact sequence, which looks approximately like

\[ 1 \to A \to B \to C \to D \to E \to F \to \ldots \]

In my paper, all these letters are actually longer mathematical expressions (cohomology groups). In one paper, this sequence fits nicely on the page, but in the other, I get an hbox overflow error.

I immediately thought of breqn, but the result of using

\begin{dmath*}
  1 \to A \to B \to C \to D \to E \to F \to \ldots
\end{dmath*}

is that I get a linebreak at every \to. This is not what I want. There should be just 1 linebreak (if needed), and it should automatically be chosen at the \to between C and D.

How do I accomplish this?

Answer 1

\documentclass{article}
\usepackage[textwidth=5cm]{geometry}% just for the example
\usepackage{breqn}

\begin{document}

\begin{dmath*}
 {1 \to A \to B \to C} \to {D \to E \to F \to \ldots}
\end{dmath*}

\end{document}

Answer 2

If you use inline rather than display math it would break automatically without needing any packages.

\documentclass{article}

\begin{document}

\def\tst{ 1 \to A \to B \to C \to D \to E \to F \to \ldots }


\fbox{\parbox{2cm}{$\displaystyle \tst $}}

\fbox{\parbox{3cm}{$\displaystyle \tst $}}

\fbox{\parbox{4cm}{$\displaystyle \tst $}}

\fbox{\parbox{5cm}{$\displaystyle \tst $}}

\fbox{\parbox{6cm}{$\displaystyle \tst $}}

\fbox{\parbox{7cm}{$\displaystyle \tst $}}

\end{document}