# Starting a theorem or a proof with an equation and vertical spacing [closed]

Is it bad practice to begin the statement of a theorem or of a proof with an equation? If it is acceptable, what is your opinion on the resulting spacing in the three cases, in the code below?

In the case of the statement of the first two facts my desired result would be to have the equation(s) starting on the same line as Fact 0.1 etc.

For the proof, I am not sure whether it looks fine this way, or whether it would be better typesetting to have the equations starting on the same line as Proof.

And in both cases I am wondering what would be the best way to achieve these changes.

\documentclass[draft,11pt]{article}
\sloppy

\usepackage{amsmath,amsthm,amssymb}

\begin{document}

\newcommand{\diam}[1]{\ensuremath{\langle #1 \rangle}}

\newtheorem{theorem}{Theorem}[section]
\newtheorem{fact}[theorem]{Fact}
\newcommand{\N}{\ensuremath{\mathsf{N}}}

\begin{fact}\label{fact:stillnotguarded}
\begin{equation*}
\text{ST}_x([!\N]\diam{a}[!\N]\diam{b}p) \textup{ is not guarded.}
\end{equation*}
\end{fact}

\medskip

\begin{fact}\label{fact:stillnotguarded}
\begin{align*}
\text{ST}_x([!\N]\diam{a}[!\N]\diam{b}p) \textup{ is not guarded.}\\
\text{ST}_x([!\N]\diam{a}[!\N]\diam{b}p) \textup{ is loosely guarded.}
\end{align*}
\end{fact}

\medskip

\begin{fact}\label{fact:notguarded}
$\text{ST}_x([!\N]\diam{a}[!\N]\diam{b}p)$ is not guarded.
\end{fact}
\begin{proof}
\begin{align*}
& ST_x([!\N]\diam{a}[!\N]\diam{b}p)\\
& = ST_x(\diam{a}[!\N]\diam{b}p^x)\\
& = \exists y (\N(x,y) \wedge R_a(x,y) \wedge
ST_y([!\N]\diam{b}p^x))\\
& = \exists y (\N(x,y) \wedge R_a(x,y) \wedge ST_y(\diam{b}p^{xy}))\\
& = \exists y (\N(x,y) \wedge R_a(x,y) \wedge (\exists z(\N(y,z) \wedge R_b(y,z)        \wedge ST_y(p^{xy}))))\\
& = \exists y (\N(x,y) \wedge R_a(x,y) \wedge (\exists z(\N(y,z) \wedge R_b(y,z) \wedge R_p(y)))) \qedhere
\end{align*}
\end{proof}

\end{document}


## closed as primarily opinion-based by Andrew Swann, Stefan Pinnow, Mensch, TeXnician, BobyandbobNov 14 '17 at 17:08

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

• In my opinion is better to start writing a little bit even few words to prepare what is coming next. For example Considering... – Sigur Jan 21 '14 at 15:08
• In the first two I'd rather write them undisplayed. But I have nothing against them being displayed. Same with the proof. It looks better if at least a little bit of text starts it, but if there is no need for it, then that is fine., But I do not think it would look good to have the formulas displayed and have the first line on the same line as the theorem/proof header, that is not nice. – daleif Jan 21 '14 at 15:09
• It is bad practice, in my opinion. Unless you're doing formal logic, theorems and proofs should start with text. – egreg Jan 21 '14 at 15:12