% Golden example -- a subst chain that must be seen, not just aligned.
%   ../scripts/build.sh subst-chain.tex
\documentclass[border=10pt]{standalone}
\usepackage[cjk]{superderive}

\sdsetrole{live}{sdTeal}

\begin{document}
\begin{tikzpicture}
\sdstage{D1}{换元让积分内部对齐}
\sdrow{R1}
  \sdbox[role=keep]{x}{$u$}
  \sdsubst[role=live]{s1}{u}{x^2}
  \sdstep[role=rewrite]{s2}{\int_0^1 x\,e^{x^2}\,dx}{\tfrac12\int_0^1 e^u\,du}
\sdrowend
\sdbbox{all}
\sdtopformula{F}{$\int_0^1 x\,e^{x^2}\,dx = \tfrac12\int_0^1 e^u\,du$}
\sdmeaningbox{mb}{120mm}{all}
  {换元是恒等改写，不改值}
  {令 $u=x^2$，则 $du=2x\,dx$}
  {上下限随 $u$ 一起换掉}
\end{tikzpicture}
\end{document}