\def\mathop:prefix#1{%
\Configure{mathop}{*}{}{}%
{\Configure{mathop}{*}{\string\mathop\l:brace}{\r:brace}{}}}
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The nested configuration of mathop is needed for cases similar to that of \log i.
$$ \sum_a^b =\log 2 $$
\pend:def\n:iint:{\ifDisplayMath\mathop:prefix{mathsize="big"}\fi}
\pend:def\n:iiint:{\ifDisplayMath\mathop:prefix{mathsize="big"}\fi}
\pend:def\n:idotsint:{\ifDisplayMath\mathop:prefix{mathsize="big"}\fi}
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\def\:tempd#1#2{%
\expandafter\def\csname #1\endcsname{\mathchar"13#2}%
\MathSymbol\mathop{#1}%
\expandafter\def\csname #1:limits\endcsname{\expandafter
\:same \math:sym\mathop{#1}\limits}%
\expandafter\def\csname #1:nolimits\endcsname{\expandafter
\:same \math:sym\mathop{#1}\nolimits}%
\expandafter\edef\csname n:#1:\endcsname{\noexpand\ifDisplayMath
\noexpand\expandafter \expandafter\noexpand
\csname #1:limits\endcsname
\noexpand\else \noexpand\expandafter
\expandafter\noexpand
\csname #1:nolimits\endcsname\noexpand\fi}%
\expandafter\pend:def\csname n:#1:\endcsname{\ifDisplayMath
\mathop:prefix{mathsize="big"}\fi}%
}
\:tempd{bigcap}{54}
\:tempd{bigcup}{53}
\:tempd{bigodot}{4A}
\:tempd{bigoplus}{4C}
\:tempd{bigotimes}{4E}
\:tempd{bigsqcup}{46}
\:tempd{biguplus}{55}
\:tempd{bigvee}{57}
\:tempd{bigwedge}{56}
\:tempd{coprod}{60}
\:tempd{intop}{52}
\:tempd{ointop}{48}
\:tempd{prod}{51}
\:tempd{sum}{50}
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\def\math:sym#1#2{{\relax\ifmmode \expandafter#1\fi
{\ifmmode\HCode{\string#1\l:brace}\fi
\csname a:#2\endcsname
\ifmmode\HCode{\r:brace}\fi}}}
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\ifx \ilimits@\o:nolimits:
\let\ilimits@\nolimits
\fi
\ifx \ilimits@\o:nolimits:
\let\slimits@\nolimits
\fi
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