Like the OP in Is it possible to skip the first line in a theorem environment?, I would like to be able to skip a line after the word "Proof" so that the first line of the proof is actually part of its own paragraph. For whatever reason the \leavevmode command suggested in the answer to the referenced question doesn't always work; it only seems to work whenever the body of the proof consists of an enumeration. I'm just using the amsthm package with the default settings. Is there a command that can be issued at the beginning of the proof that will allow me to skip a line? Of course, like the OP, I've tried \\ and variants thereof and am only rewarded with the obnoxious "There's no line here to end" error.
[Tex/LaTex] Skipping line after “Proof” in proof environment
line-breakingtheorems
Related Solutions
One possibility would be to redefine the proof anvironment as defined in amsthm.sty (the definition uses \topsep6\p@\@plus6\p@\relax, so you could make some changes there). Another approach would be to use the front-end thmtools to define a new theorem-like structure behaving like the standard proof environment, but using the spaceabove key to control the vertical space above it. The following example illustrates this second approach and shows the different spacing for the new prf environment and the standard proof environment:
\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools}
\declaretheorem{theorem}
\declaretheoremstyle[%
spaceabove=-6pt,%
spacebelow=6pt,%
headfont=\normalfont\itshape,%
postheadspace=1em,%
qed=\qedsymbol%
]{mystyle}
\declaretheorem[name={Proof},style=mystyle,unnumbered,
]{prf}
\begin{document}
\begin{theorem}
A really important result.
\end{theorem}
\begin{prf}
And its proof with less space above.
\end{prf}
\begin{theorem}
A really important result.
\end{theorem}
\begin{proof}
And its proof with too much space above.
\end{proof}
\end{document}
Given that the theorem and proof environments are quite separate, it's indeed a bit tricky to forbid categorically all pagebreaks between them. All I can suggest is that you load the package needspace and insert the command
\Needspace{3\baselineskip}
close to the end of the statement of the theorem/corollary/whatever; note the uppercase N at the start of the macro. According to the manual of the needspace package, the command "\Needspace{} is less efficient [than \needspace{}] but reserves the requested space exactly. It should only be used between paragraphs." Given that you're basically facing this situation, you may want to give it a try.
You'll probably have to practice a bit to determine the best placement of this command and the number of baseline skips you require in order to always get at least two lines of the proof statement to show up on the same page as the associated theorem.
Best Answer
If this is to apply to all the
proofenvironments in your document, you can redefine theproofenvironment to add\\*after the proof name has been written; here's such a redefinition (a\mbox{}will be necessary before\\*):