Limits of Sub- snd Super- Scripts

<..limits sub, sup, subsup ..>

\Configure{nolimits}{\HCode{\string\nolimits\space}}
\Configure{limits}
    {\let<.restore SUB .>=\:UnDef
     \let<.restore SUP .>=\:UnDef
     \ifx \:temp\sp <.conf limits SUP .>\else
     \ifx \:temp\sb <.conf limits SUB .>\fi\fi
     <.conf limits SUBSUP .>%
    }

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<..conf limits SUBSUP ..>

<.save pre-limits SUBSUP .>%
\Configure{SUBSUP}
    {\ifx <.restore SUB .>\:UnDef\else  <.restore SUB .>\fi
     \ifx <.restore SUP .>\:UnDef\else  <.restore SUP .>\fi
     <.restore pre-limits SUBSUP .>%
     \Send{BACK}{\l:brace}\HCode{\r:brace
                             \string_\l:brace}\trap:base
    }
    {\HCode{\r:brace\string^\l:brace}\trap:base}
    {\HCode{\r:brace}}

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<..save pre-limits SUBSUP ..>

\let\pl:SUBSUP=\SUBSUP:

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<..restore pre-limits SUBSUP ..>

\ifx \pl:SUBSUP\:UnDef \else
\let\SUBSUP:=\pl:SUBSUP
\fi

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<..limits sub, sup, subsup ..>+

\ifx \a:putSUB\:UnDef \else
    \pend:def\a:putSUB{\ifx \pl:SUBSUP\:UnDef\else
          \let\SUBSUP:=\pl:SUBSUP
          \let\pl:SUBSUP=\:UnDef
       \fi}%
\fi
\ifx \a:putSUP\:UnDef \else
    \pend:def\a:putSUP{\ifx \pl:SUBSUP\:UnDef\else
          \let\SUBSUP:=\pl:SUBSUP
          \let\pl:SUBSUP=\:UnDef
       \fi}%
\fi

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<..conf limits SUP ..>

<.save pre-limits SUP .>%
\Configure{SUP}
    {<.open external limits SUP .>\bgroup
      <.restore pre-limits SUBSUP .>%
      <.conf second limits SUP .>\trap:base}
    {}%

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<..save pre-limits SUP ..>

\def\pl:SUP{\Configure{SUP}}%
\expandafter\append:def
\expandafter\pl:SUP\expandafter{\expandafter{\a:SUP}}%
\expandafter\append:def
\expandafter\pl:SUP\expandafter{\expandafter{\b:SUP}}%

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<..conf second limits SUP ..>

\Configure{SUP}
    {<.open intermediate limits SUP .>\bgroup
     <.conf third limit SUP .>\trap:base}
    {\egroup<.close external limits SUP .>}%

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<..conf third limit SUP ..>

\Configure{SUP}
{<.open internal limits SUP .>\bgroup \trap:base}
{\egroup <.close internal limits SUP .>}%

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<..open external limits SUP ..>

\Send{BACK}{\l:brace}\HCode{\r:brace\string^\l:brace}\trap:base

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<..close external limits SUP ..>

\HCode{\r:brace}\aftergroup<.restore SUP .>%

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<..restore SUP ..>

\pl:SUP

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<..open intermediate limits SUP ..>

\Send{BACK}{\l:brace}\HCode{\r:brace\string^\l:brace}\trap:base

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<..open internal limits SUP ..>

\Send{BACK}{\l:brace}\HCode{\r:brace\string^\l:brace}%

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<..close internal limits SUP ..>

\HCode{\r:brace}%

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<..conf limits SUB ..>

<.save pre-limits SUB .>%
\Configure{SUB}
    {<.open external limits SUB .>\bgroup
      <.restore pre-limits SUBSUP .>%
      <.conf second limits SUB .>\trap:base}
    {}%

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<..save pre-limits SUB ..>

\def\pl:SUB{\Configure{SUB}}%
\expandafter\append:def
\expandafter\pl:SUB\expandafter{\expandafter{\a:SUB}}%
\expandafter\append:def
\expandafter\pl:SUB\expandafter{\expandafter{\b:SUB}}%

-_-_-

<..conf second limits SUB ..>