ご質問はこちらへ

\documentclass[a4paper]{article}

\usepackage{amsmath, amssymb}

\usepackage{latexsym}

\usepackage{overcite}

\usepackage{amsthm}

\usepackage{ulem}

\begin{document}

\begin{align}

\sum_{spins}|\bar{v}(p')\gamma ^\mu(\frac{1+\gamma ^5}{2})u(p)|^2 &=\sum_{spins}\bar{v}(p')\gamma^{\mu}(\frac{1+\gamma^5}{2})u(p)\bar{u}(p)\gamma^{\nu}(\frac{1+\gamma^5}{2})v(p') \\

&=\mathrm{tr}[\xout{p'}

\gamma^{\mu}(\frac{1+\gamma^5}{2})\xout{p}\gamma^{\nu}(\frac{1+\gamma^5}{2})] \\

&=\mathrm{tr}[\xout{p'}\gamma^{\mu}\xout{p}\gamma^{\nu}(\frac{1+\gamma^5}{2})] \\

&=2(p'^{\mu}p^{\nu}-p'^{\nu}p^{\mu}-g^{\mu\nu}p\cdot p'-i\epsilon^{\alpha\mu\beta\nu}p'_{\alpha}p_{\beta})

\end{align}

\end{document}

---------------------------------------------------------------------------------------

logです。

---------------------------------------------------------------------------------------

This is ptex2pdf[.lua] version 20200520.0.

Processing Peskin519.tex

This is e-pTeX, Version 3.14159265-p3.8.3-191112-2.6 (utf8.sjis) (TeX Live 2020/W32TeX) (preloaded format=platex)

restricted \write18 enabled.

entering extended mode

(./Peskin519.tex

pLaTeX2e <2020-04-12> (based on LaTeX2e <2020-02-02> patch level 5)

L3 programming layer <2020-09-24>

(c:/texlive/2020/texmf-dist/tex/latex/base/article.cls

Document Class: article 2019/12/20 v1.4l Standard LaTeX document class

(c:/texlive/2020/texmf-dist/tex/latex/base/size10.clo))

(c:/texlive/2020/texmf-dist/tex/latex/amsmath/amsmath.sty

For additional information on amsmath, use the `?' option.

(c:/texlive/2020/texmf-dist/tex/latex/amsmath/amstext.sty

(c:/texlive/2020/texmf-dist/tex/latex/amsmath/amsgen.sty))

(c:/texlive/2020/texmf-dist/tex/latex/amsmath/amsbsy.sty)

(c:/texlive/2020/texmf-dist/tex/latex/amsmath/amsopn.sty))

(c:/texlive/2020/texmf-dist/tex/latex/amsfonts/amssymb.sty

(c:/texlive/2020/texmf-dist/tex/latex/amsfonts/amsfonts.sty))

(c:/texlive/2020/texmf-dist/tex/latex/base/latexsym.sty)

(c:/texlive/2020/texmf-dist/tex/latex/cite/overcite.sty)

(c:/texlive/2020/texmf-dist/tex/latex/cite/cite.sty)

(c:/texlive/2020/texmf-dist/tex/latex/amscls/amsthm.sty)

(c:/texlive/2020/texmf-dist/tex/generic/ulem/ulem.sty)

(c:/texlive/2020/texmf-dist/tex/latex/l3backend/l3backend-dvips.def)

(./Peskin519.aux) (c:/texlive/2020/texmf-dist/tex/latex/amsfonts/umsa.fd)

(c:/texlive/2020/texmf-dist/tex/latex/amsfonts/umsb.fd)

(c:/texlive/2020/texmf-dist/tex/latex/base/ulasy.fd)

Runaway argument?

\sum _{spins}|\bar {v}(p')\gamma ^\mu (\frac {1+\gamma ^5}{2})u(p)|^\ETC.

! Paragraph ended before \align was complete.

<to be read again>

\par

l.10

?

\documentclass[12pt,fleqn,dvipdfmx]{jsbook}

\newenvironment{kakko}%

{\vspace{-8mm}\begin{enumerate}[(1)]}

{\end{enumerate}\vspace{-5mm}}

\begin{document}

\begin{kakko}

\item アイテム1

\item アイテム2

\end{kakko}

\end{document}

以上をpLaTeXで出力すると

LaTeX Error: Something's wrong--perhaps a missing \item.

となり読み込まれません。

どうしてでしょうか。

なお、newenvironment自体が使えないということはございません。