unwanted vertical space after \item

Question

If I run the following code

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{color}
\usepackage{amsmath}
\usepackage{amsthm}
\def\myproof#1{{\color{blue}\begin{proof}#1 \end{proof}}}

\begin{document}
\begin{enumerate}
  \item 1
  \myproof{sdf}
  \item Thisis Thisis This is This is This is This is This is This is This is This.
  \myproof{sdf}
\end{enumerate}
\end{document}

Then, I would get

which has a bad vertical spacing right above the second Proof.

I can solve this problem by adding % or \leavevmode right after This.

But is there any way I can prevent this in the first place by changing the definition of \myproof?

Answer 1

You need \par in front of \color{blue}.

What happens in your example is that the space coming from the endline is followed by {\color{blue}\begin{proof}...} and the \par that's issued by \begin{proof} (actually by \trivlist, but it's not important) cannot remove it. So a line consisting of just one space is built.

This can be seen by the following example, where you see that masking the endline with % removes the spurious line.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{color}
\usepackage{amsmath}
\usepackage{amsthm}
\def\myproof#1{{\color{blue}\begin{proof}#1 \end{proof}}}

\begin{document}
\begin{enumerate}
  \item 1
  \myproof{sdf}
  \item Thisis Thisis This is This is This is This is This is This is This is This.%
  \myproof{sdf}
  \item Thisis Thisis This is This is This is This is This is This is This is This.
  \myproof{sdf}
\end{enumerate}
\end{document}

If we modify it as

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{color}
\usepackage{amsmath}
\usepackage{amsthm}

\newcommand\myproof[1]{\par{\color{blue}\begin{proof}#1 \end{proof}}}

\begin{document}
\begin{enumerate}
  \item 1
  \myproof{sdf}
  \item Thisis Thisis This is This is This is This is This is This is This is This.%
  \myproof{sdf}
  \item Thisis Thisis This is This is This is This is This is This is This is This.
  \myproof{sdf}
\end{enumerate}
\end{document}

you can see that the % is no longer necessary.

My preferred way would be

\newenvironment{blueproof}{\par\color{blue}\proof}{\endproof}

using

\begin{enumerate}
  \item 1
  \begin{blueproof}
  sdf
  \end{blueproof}
  \item Thisis Thisis This is This is This is This is This is This is This is This.
  \begin{blueproof}
  sdf
  \end{blueproof}
\end{enumerate}
\end{document}