# Nice line-break in inline math within theorem environment

This is my first question here, I hope it's not bad (please bear with me if it is).

I have quite a specific problem concerning inline math and theorem environment. In general, I want to obtain the behavior of \align or amsmath \multline in inline math and theorem environment (I am using LNCS style file, so it is actually either definition or \spnewtheorem).

To be more specific: I have a long logical formula within definition with a normal line break which makes the formula not very clear (see image below).

\begin{definition}
$UNT_{2}(a,b) \equiv_{\text{df}}\exists t_1\exists t_3 > t_1[(a \in t_1) \land (b \in t_3) \land (a \not\in t_3) \land \forall t_2( t_1<t_2<t_3 \to a \in t_2)]$
\end{definition}


I would like the formula to start on the same line as "Definition 3" but:

1. In a new line the formula should be aligned to the \equiv sign (I like the approach taken here but I am not sure how to make it work with \equiv)
2. I would like to be able to control (at least to some extent) on which operator the formula breaks

I am aware of breqn package but it does not really work with inline math nor do the methods provided by amsmath. I tried using description but it doesn't help.
Of course I could just break my expression into a few expressions and try to make it work with \\ and \, but this seems very bad.

Any help would be very appreciated.

You can use aligned. I used amsthm for defining the environment, you should be able to adapt to llncs.

\documentclass{article}
\usepackage{amsmath,amsthm}

\theoremstyle{definition}
\newtheorem{definition}{Definition}

\begin{document}

\begin{definition}
\begin{aligned}[t] \mathit{UNT}_{2}(a,b) \equiv_{\mathrm{df}}{} & \exists t_1\exists t_3 > t_1[(a \in t_1) \land (b \in t_3) \land (a \not\in t_3) \land {}\\ & \forall t_2( t_1<t_2<t_3 \to a \in t_2)] \end{aligned}
\end{definition}

\end{document}


The alignment point has been set after the equivalence symbol; for this it's necessary to have {} in order to ensure correct spacing.

• Cool, this works out of the box. Thank you very much. That was fast! (I would love to upvote, but you'll have to wait for my reputation to rise :)) – jjj Mar 14 '16 at 10:36