如果没有前面的文本，则删除 tcolorbox 环境中的第一个 \tcbline

Question

我正在尝试定义自己的证明环境，将证明分为几个步骤。我使用tcolorbox包装proof环境，并用 分隔各个步骤\tcbline*。但是，在此之前，我还重新定义了proof环境以摆脱“证明：”前缀。

\documentclass{article}

\usepackage{amsthm}
\usepackage[many]{tcolorbox}

% Renew proof environment to avoid "Proof." at the start.
\renewenvironment{proof}{\unskip\ignorespaces}{\hfill \qedsymbol}

% Creates a heading for a step of a proof.
\NewDocumentCommand{\proofpart}{m}{\tcbline*\noindent\textbf{#1}\vspace{0.25em}\newline}

% Wrap the proof environment in a tcolorbox.
\tcolorboxenvironment{proof}{}

\begin{document}

\begin{proof}
\proofpart{First (should not have line above)}
abc
\proofpart{Second (should have line above)}
abc
\proofpart{Third (should have line above)}
abc
\end{proof}

\end{document}

看起来像这样：

\tcbline*如果前面没有文本，我希望不显示第一个。有办法实现吗？

Answer 1

如果上部第一段还未开始，则尝试跳过\tcbline*。\proofpart

\documentclass{article}

\usepackage{amsthm}
\usepackage[many]{tcolorbox}

\newif\ifmytcbupperstarted
\tcbsetforeverylayer{
  code={\mytcbupperstartedfalse},
  before upper pre={\AddToHookNext{para/begin}{\mytcbupperstartedtrue}}
}

% Renew proof environment to avoid "Proof." at the start.
\renewenvironment{proof}{\unskip\ignorespaces}{\hfill \qedsymbol}

% Creates a heading for a step of a proof.
\NewDocumentCommand{\proofpart}{m}{%
  \ifmytcbupperstarted\tcbline*\fi
  \noindent\textbf{#1}\vspace{0.25em}\newline}

% Wrap the proof environment in a tcolorbox.
\tcolorboxenvironment{proof}{}

\begin{document}

\begin{proof}
\proofpart{First (should not have line above)}
abc
\proofpart{Second (should have line above)}
abc
\proofpart{Third (should have line above)}
abc
\end{proof}

\begin{tcolorbox}
  \ifmytcbupperstarted\tcbline\fi
  layer 1
  \tcbline
  layer 1
  \begin{tcolorbox}
    \ifmytcbupperstarted\tcbline\fi
    layer 2
    \tcbline
    layer 2
  \end{tcolorbox}
\end{tcolorbox}

\end{document}

原始版本

\tcbset{before upper pre={\AddToHookNext{para/begin}{\mytcbupperstartedtrue}}}

仅适用于最外层的tcolorboxes。现在修订的版本也适用于嵌套的tcolorboxes。