path: root/tex/context/base/math-ini.mkiv

%D \module
%D   [       file=math-ini,
%D        version=2008.01.02,
%D          title=\CONTEXT\ Math Macros,
%D       subtitle=Initializations,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright=PRAGMA]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{ConTeXt Math Macros / Initializations}

%D This module provides namespaces for math fonts, thereby
%D permitting mixed usage of math fonts. Although not strictly
%D needed, we also provide a family name mapping mechanism as
%D used in the (original) AMS math definition files, but here
%D these names can recursively be remapped and if needed,
%D dynamically be changed. We've tried to minimize the number
%D of definition commands and use plain \TEX\ definitions as
%D fallback. We've tried to follow a couple of conventions
%D from plain and AMS math in order to achieve backward
%D compatinility. We also kept an eye on future usage of these
%D modules in the perspective of MathML and unicode fonts.

\unprotect

\ifx\v!compact\undefined \def\v!compact{compact} \fi

%D New:

\let\startimath\Ustartmath         \let\stopimath \Ustopmath
\let\startdmath\Ustartdisplaymath  \let\stopdmath \Ustopmath

%D We move these definitions into the format:

% test [[\char948 \ctxlua{tex.sprint(utf.char(948))}]]
% test $[[\char948 \ctxlua{tex.sprint(utf.char(948))}]]$

\registerctxluafile{math-ini}{1.001}
\registerctxluafile{math-dim}{1.001}
\registerctxluafile{math-ent}{1.001}
\registerctxluafile{math-ext}{1.001}
\registerctxluafile{math-vfu}{1.001}
\registerctxluafile{math-map}{1.001}
\registerctxluafile{math-noa}{1.001}
\registerctxluafile{math-tag}{1.001}

\definesystemattribute[mathalphabet]        \chardef\mathalphabetattribute    \dogetattributeid{mathalphabet}
\definesystemattribute[mathsize]            \chardef\mathsizeattribute        \dogetattributeid{mathsize}
\definesystemattribute[mathpunctuation]     \chardef\mathpunctuationattribute \dogetattributeid{mathpunctuation}
\definesystemattribute[mathgreek]           \chardef\mathgreekattribute       \dogetattributeid{mathgreek}
\definesystemattribute[mathalternate]       \chardef\mathalternateattribute   \dogetattributeid{mathalternate}

% experiment

% Normally this is applied to only one character.
%
% $ABC$ $\cal ABC$ $\mathaltcal ABC$

\def\mathalternate#1{\ctxlua{mathematics.setalternate(0,"#1")}} % fam 0

\def\mathaltcal{\mathalternate{cal}\cal} % ss01 in xits

% todo: only in mmode

\unexpanded\def\mathgreekupright{\attribute\mathgreekattribute22 }
\unexpanded\def\mathgreekitalic {\attribute\mathgreekattribute33 }
\unexpanded\def\mathgreekdefault{\attribute\mathgreekattribute\attributeunsetvalue}

\let\mathgreeknormal\mathgreekupright
\let\mathgreeknone  \mathgreekdefault

\def\setmathattribute#1#2{\ifmmode\ctxlua{mathematics.syncboth ("#1","#2")}\fi}
\def\setmathalphabet   #1{\ifmmode\ctxlua{mathematics.syncname ("#1")}\fi}
\def\setmathstyle      #1{\ifmmode\ctxlua{mathematics.syncstyle("#1")}\fi}

\unexpanded\def\mr            {\setmathattribute{regular}{tf}}

\unexpanded\def\mathdefault   {\setmathattribute{regular}{it}}
\unexpanded\def\mathscript    {\setmathalphabet{script}}
\unexpanded\def\mathfraktur   {\setmathalphabet{fraktur}}
\unexpanded\def\mathblackboard{\setmathalphabet{blackboard}}

\unexpanded\def\mathrm{\setmathattribute{rm}{tf}}
\unexpanded\def\mathss{\setmathattribute{ss}{tf}}
\unexpanded\def\mathtt{\setmathattribute{tt}{tf}}

\unexpanded\def\mathtf{\setmathstyle{tf}}
\unexpanded\def\mathbf{\setmathstyle{bf}}
\unexpanded\def\mathsl{\setmathstyle{sl}}
\unexpanded\def\mathit{\setmathstyle{it}}
\unexpanded\def\mathbs{\setmathstyle{bs}}
\unexpanded\def\mathbi{\setmathstyle{bi}}

\let\tfmath\mathtf % maybe a grouped command
\let\bfmath\mathbf
\let\slmath\mathsl
\let\itmath\mathit
\let\bsmath\mathbs
\let\bimath\mathbi

\let\Bbb\mathblackboard

\unexpanded\def\frak      {\ifmmode\expandafter\mathfraktur   \fi}
\unexpanded\def\cal       {\ifmmode\expandafter\mathscript    \fi}
\unexpanded\def\bbd       {\ifmmode\expandafter\mathblackboard\fi}
\unexpanded\def\blackboard{\ifmmode\expandafter\mathblackboard\fi}
\unexpanded\def\fraktur   {\ifmmode\expandafter\mathfraktur   \fi}
\unexpanded\def\gothic    {\ifmmode\expandafter\mathfraktur   \fi}

\unexpanded\def\mathcal #1{{\mathscript    #1}}  % for AMS compatibility
\unexpanded\def\mathfrak#1{{\mathfraktur   #1}}  % for AMS compatibility
\unexpanded\def\mathbb  #1{{\mathblackboard#1}}  % for AMS compatibility

\let\normalmr\mr

% \prependtoks
%     \let\mr\normalmr
%     \let\rm\mathrm \let\ss\mathss \let\tt\mathtt
%     \let\tf\mathtf \let\bf\mathbf \let\it\mathit \let\sl\mathsl \let\bi\mathbi \let\bs\mathbs
%     \let\frak\mathfraktur \let\cal\mathscript \let\bbd\mathblackboard
%     \mathdefault
% \to \everymathematics

\let\normaltf\tf \unexpanded\def\tf{\ifmmode\mathtf\else\normaltf\fi}
\let\normalbf\bf \unexpanded\def\bf{\ifmmode\mathbf\else\normalbf\fi}
\let\normalit\it \unexpanded\def\it{\ifmmode\mathit\else\normalit\fi}
\let\normalsl\sl \unexpanded\def\sl{\ifmmode\mathsl\else\normalsl\fi}
\let\normalbi\bi \unexpanded\def\bi{\ifmmode\mathbi\else\normalbi\fi}
\let\normalbs\bs \unexpanded\def\bs{\ifmmode\mathbs\else\normalbs\fi}

\let\normalrm\rm \unexpanded\def\rm{\ifmmode\mathrm\else\normalrm\fi}
\let\normalss\ss \unexpanded\def\ss{\ifmmode\mathss\else\normalss\fi}
\let\normaltt\tt \unexpanded\def\tt{\ifmmode\mathtt\else\normaltt\fi}
                 \unexpanded\def\mr{\ifmmode            \normalmr\fi}

\prependtoks
%     \let\mr\normalmr
%     \let\rm\mathrm \let\ss\mathss \let\tt\mathtt
%     \let\tf\mathtf \let\bf\mathbf \let\it\mathit \let\sl\mathsl \let\bi\mathbi \let\bs\mathbs
%     \let\frak\mathfraktur \let\cal\mathscript \let\bbd\mathblackboard
    \mathdefault
\to \everymathematics

%D \macros
%D   {boldsymbol}
%D
%D To be done.

\let\mathboldsymbol\relax % yet unsupported, will be

\def\boldsymbol
  {\mathortext\mathboldsymbol\bold}

%D Helpers:

\def\utfmathclass  #1{\ctxlua{tex.sprint(mathematics.utfmathclass  ("#1"))}}
\def\utfmathstretch#1{\ctxlua{tex.sprint(mathematics.utfmathstretch("#1"))}}
\def\utfmathcommand#1{\ctxlua{tex.sprint(mathematics.utfmathcommand("#1"))}}
\def\utfmathfiller #1{\ctxlua{tex.sprint(mathematics.utfmathfiller ("#1"))}}

% \def\utfmathclassdefault  #1#2{\ctxlua{
%     tex.sprint(mathematics.utfmathclass("#1","#2"))
% }}
%
% \def\utfmathcommanddefault#1#2#3{\ctxlua{
%     local cmd = mathematics.utfmathcommand("#1","") or ""
%     if cmd == "" then
%         commands.cs("#2","#3")
%     else
%         commands.cs(cmd)
%     end}}

% % %

\def\@@mathlimopcomm #1{\mathop{#1}} %no \limits
\def\@@mathnolopcomm #1{\mathop{#1}\nolimits}
\def\@@mathboxcomm   #1{\dontleavehmode\hbox\Ustartmath\mathsurround\zeropoint#1\Ustopmath}
\def\@@mathchoicecomm#1{[todo #1]}

\chardef\mathordcode    = 0  \let\mathordcomm     \mathord
\chardef\mathopcode     = 1  \let\mathopcomm      \mathop
\chardef\mathbincode    = 2  \let\mathbincomm     \mathbin
\chardef\mathrelcode    = 3  \let\mathrelcomm     \mathrel
\chardef\mathopencode   = 4  \let\mathopencomm    \mathopen
\chardef\mathclosecode  = 5  \let\mathclosecomm   \mathclose
\chardef\mathpunctcode  = 6  \let\mathpunctcomm   \mathpunct
\chardef\mathalphacode  = 7  \let\mathalphacomm   \firstofoneargument
\chardef\mathinnercode  = 0  \let\mathinnercomm   \mathinner
\chardef\mathnothingcode= 0  \let\mathnothingcomm \firstofoneargument
\chardef\mathlimopcode  = 1  \let\mathlimopcomm   \@@mathlimopcomm
\chardef\mathnolopcode  = 1  \let\mathnolopcomm   \@@mathnolopcomm
\chardef\mathchoicecode = 0  \let\mathchoicecomm  \@@mathchoicecomm
\chardef\mathboxcode    = 0  \let\mathboxcomm     \@@mathboxcomm

\chardef\mathaccentcode = 8
\chardef\mathradicalcode= 9

\def\puremathcode#1{\the\csname math#1code\endcsname}
\def\puremathcomm#1{\csname     math#1comm\endcsname}

% \startlines
% $\mathopnolimits{\rm d}x$
% $\mathopnolimits{\kern\zeropoint \rm d}x$
% $\puremathcomm{nolop}{\rm d}x$
% $\puremathcomm{nolop}{\kern\zeropoint\rm d}x$
% \blank
% $\puremathcomm{nolop}{\mr d}x$
% $\puremathcomm{nolop}{\kern\zeropoint\mr d}x$
% $\mathop{\kern\zeropoint\mr d}x$
% $\mathopnolimits{\kern\zeropoint d}x$
% \stoplines

% this will be sorted out:

\let\mathcharacter           \getvalue
\let\textcharacter           \getvalue
\unexpanded\def\definefamilysynonym     {\dotripleempty\dodefinefamilysynonym}
\def\dodefinefamilysynonym   [#1][#2][#3]{}
\unexpanded\def\definemathsymbol        {\dosixtupleempty\dodefinemathsymbol}
\def\dodefinemathsymbol      [#1][#2][#3][#4][#5][#6]{}
\unexpanded\def\definemathcharacter     {\dosixtupleempty\dodefinemathcharacter}
\def\dodefinemathcharacter   [#1][#2][#3][#4][#5][#6]{}

\unexpanded\def\definemathcommand
  {\dotripleempty\dodefinemathcommand}

\def\dodefinemathcommand[#1][#2][#3]#4% command class args meaning
  {\ifthirdargument
     \processaction
       [#3]
       [one=>\setuvalue{#1}##1{\puremathcomm{#2}{#4{##1}}},
        two=>\setuvalue{#1}##1##2{\puremathcomm{#2}{#4{##1}{##2}}}]%
   \else\ifsecondargument
     \setuvalue{#1}{\puremathcomm{#2}{#4}}%
   \else
     \setuvalue{#1}{\puremathcomm{nothing}{#4}}%
   \fi\fi}

%D Moved from font-ini.mkiv:
%D
%D \macros
%D   {mf,mbox,enablembox,mathop}
%D
%D Todo:

\unexpanded\def\mf
  {\csname\fontalternative\endcsname}

\let\normalmathop\mathop

\unexpanded\def\mathop
  {\normalmathop
   \bgroup
   \let\rm\mf
   \let\next=}

\def\normalmbox
  {\normalhbox\bgroup\mf
   \dowithnextbox{\flushnextbox\egroup}\normalhbox}

\def\mbox % we cannot add \dontleavehmode ... else no \setbox0\mbox possible
  {\ifmmode\normalmbox\else\normalhbox\fi}

\unexpanded\def\enablembox
  {\appendtoks
     \ifx\normalhbox\undefined\let\normalhbox\hbox\fi
     \let\hbox\mbox
   \to\everymathematics}

%D needed for sin, cos etc

\let\mathfunction\firstofoneargument

\def\mfunction         #1{{\mr#1}}
\def\mfunctionlabeltext#1{{\mr\mathlabeltext{#1}}}

% \def\mlimitsfunction  #1{\mathlimopcomm{{\mr#1}}
% \def\mnolimitsfunction#1{\mathnolopcomm{{\mr#1}}

%D Taco posted this solution as response to a mail by Olivier, so
%D let's integrate it here.

\def\currentmscaledstyle{rm} % will be plugged into the typeface text=ss option

\unexpanded\def\do@mathopnolimits    #1{\mathop{\mscaledtext{#1}}\nolimits}
\unexpanded\def\do@mfunction         #1{\mscaledtext{#1}}
\unexpanded\def\do@mfunctionlabeltext#1{\mscaledtext{\mathlabeltext{#1}}}

\def\setmathfunctionstyle#1% rm ss tt (can be made faster if needed)
  {\doifsomething{#1}
     {\def\currentmscaledstyle{#1}%
      \let\mathopnolimits    \do@mathopnolimits
      \let\mfunction         \do@mfunction
      \let\mfunctionlabeltext\do@mfunctionlabeltext}}

\def\mscaledtext#1%
  {\mathchoice
     {\hbox{\csname\currentmscaledstyle\endcsname\tf  #1}}
     {\hbox{\csname\currentmscaledstyle\endcsname\tf  #1}}
     {\hbox{\csname\currentmscaledstyle\endcsname\tfx #1}}
     {\hbox{\csname\currentmscaledstyle\endcsname\tfxx#1}}}

%D We can force the way functions are typeset by manipulating the text
%D option:
%D
%D \starttyping
%D \definetypeface[iwona][ss][sans][iwona][default][encoding=texnansi]
%D \definetypeface[iwona][mm][math][iwona][default][encoding=texnansi,text=ss]
%D \stoptyping
%D
%D This hooks into the math handler with:

% no longer supported this way, has to be done with \setupmathematics
%
% \appendtoks
%     \setmathfunctionstyle\currentmathtextstyle
% \to \everybodyfont

%D Usage:
%D
%D \starttyping
%D \setmathfunctionstyle\fontstyle % or {rm} or {ss} or ..
%D \rm test $\sin{(x^{\sin(x^{\sin(x)})})}$ test
%D \ss test $\sin{(x^{\sin(x^{\sin(x)})})}$ test
%D \tt test $\sin{(x^{\sin(x^{\sin(x)})})}$ test
%D \stoptyping

%D Some goodies:

\def\Angstrom{\nomathematics{\Aring}}

%D \macros
%D   {nonknuthmode, donknuthmode}
%D
%D The underscore is frequently used in manuals but unfortunately \TEX\ prefers
%D it to be a math specific character. And since computer modern fonts didn't
%D have an underscore, one had to use commands to fake one. Nowadays we do
%D have underscores in latin modern, and since all other fonts have them, we
%D decided to get away from the restriction to use the underscore character in
%D text mode.
%D
%D \starttyping
%D \def\test#1{#1}
%D
%D \nonknuthmode $x_2$ x_2 \test{$x_2$} \test{x_2}
%D
%D \donknuthmode $x_2$ x_2 \test{$x_2$} \test{x_2}
%D \stoptyping
%D
%D The result is as expected: the first line typesets ok, while the second
%D one triggers an error message.

\newtoks\everydonknuthmode
\newtoks\everynonknuthmode

\def\nonknuthmode{\the\everynonknuthmode\let\nonknuthmode\relax}
\def\donknuthmode{\the\everydonknuthmode}

\ifdefined\normalsuber\else \def\normalsuber{_} \fi
\ifdefined\normalsuper\else \def\normalsuper{^} \fi
\ifdefined\normalaltab\else \def\normalaltab{&} \fi

\bgroup

    \catcode`_=\active
    \catcode`^=\active
    \catcode`&=\active

    \global \everynonknuthmode {\appendtoks
        \let_\normalsuber
        \let^\normalsuper
        \let&\normalaltab
    \to \everymathematics}

\egroup

\appendtoks
    \mathcode`_="8000
    \mathcode`^="8000
    \mathcode`&="8000
    \catcode`_=\@@other
    \catcode`^=\@@other
    \catcode`&=\@@other
\to \everynonknuthmode

\appendtoks
    \catcode`_=\@@subscript
    \catcode`^=\@@superscript
    \catcode`&=\@@alignment
\to \everydonknuthmode

\appendtoks
    \startextendcatcodetable\ctxcatcodes
        \catcode`_=\@@other
        \catcode`^=\@@other
        \catcode`&=\@@other
    \stopextendcatcodetable
\to \everynonknuthmode

\appendtoks
    \startextendcatcodetable\ctxcatcodes
        \catcode`_=\@@subscript
        \catcode`^=\@@superscript
        \catcode`&=\@@alignment
    \stopextendcatcodetable
\to \everydonknuthmode

%D Even more drastic:

\def\asciimode{\catcodetable\txtcatcodes\nonknuthmode}

%D Needed for unicode:

\def\nulloperator{\mathortext{\mathop{\null}}{\null}}

%D To be dealt with ...

\mathcode`\ ="8000 % \space
\mathcode`\'="8000 % ^\prime
\mathcode`\_="8000 % \_

%D \macros
%D   {setupmathematics}
%D
%D Configuration for integrals. (If needed we can speed this up and make it
%D installable; no processaction is needed then).

\newtoks\everysetupmathematics

\unexpanded\def\setupmathematics
  {\dosingleargument\dosetupmathematics}

\def\dosetupmathematics[#1]%
  {\getparameters[\??mo][#1]%
   \the\everysetupmathematics}

\def\mathematicsparameter#1{\ifcsname\??mo#1\endcsname\csname\??mo#1\endcsname\fi}

%D Memory saver:

\appendtoks
   \doifelse{\mathematicsparameter\v!compact}\v!yes
     {\ctxlua{fonts.vf.math.optional=true}}
     {\ctxlua{fonts.vf.math.optional=false}}%
\to \everysetupmathematics

\setupmathematics
  [\v!compact=no]

%D Delayed: greek.
%D
%D \starttyping
%D \usetypescript[cambria]\setupbodyfont[cambria]
%D \startTEXpage
%D     $\alpha \mathgreekupright \alpha \mathgreekitalic \alpha$
%D \stopTEXpage
%D \stoptyping

% [lc uc] normal (upright) = 2, italic = 3, none = 0/1

\setevalue{\??mo:greek:\v!normal :\v!normal}{\attribute\mathgreekattribute22 }
\setevalue{\??mo:greek:\v!normal :\v!italic}{\attribute\mathgreekattribute23 }
\setevalue{\??mo:greek:\v!normal :\v!none  }{\attribute\mathgreekattribute21 }

\setevalue{\??mo:greek:\v!italic :\v!normal}{\attribute\mathgreekattribute32 }
\setevalue{\??mo:greek:\v!italic :\v!italic}{\attribute\mathgreekattribute33 }
\setevalue{\??mo:greek:\v!italic :\v!none  }{\attribute\mathgreekattribute31 }

\setevalue{\??mo:greek:\v!none   :\v!normal}{\attribute\mathgreekattribute12 }
\setevalue{\??mo:greek:\v!none   :\v!italic}{\attribute\mathgreekattribute13 }
\setevalue{\??mo:greek:\v!none   :\v!none  }{\attribute\mathgreekattribute\attributeunsetvalue}

\appendtoks
    \csname\??mo:greek:\@@molcgreek:\@@moucgreek\endcsname
\to \everymathematics

\setupmathematics
  [lcgreek=\v!italic,
   ucgreek=\v!normal] % was: none

%D \macros
%D   {enablemathpunctuation,disablemathpunctuation}
%D
%D \startbuffer
%D \enablemathpunctuation$(1,2) (1, 2) (1{,}2) \hbox{foo, not bar}$
%D \stopbuffer
%D
%D \typebuffer
%D
%D \blank{\getbuffer}\blank

\setfalse \automathpunctuation

\def\enablemathpunctuation {\settrue \automathpunctuation}
\def\disablemathpunctuation{\setfalse\automathpunctuation}

\ifx\v!autopunctuation\undefined \def\v!autopunctuation{autopunctuation} \fi

\appendtoks
    \doifelse{\mathematicsparameter\v!autopunctuation}\v!yes\enablemathpunctuation\disablemathpunctuation
\to \everysetupmathematics

\appendtoks
    \ifconditional\automathpunctuation\attribute\mathpunctuationattribute\plusone\fi
\to \everymathematics

\setupmathematics
  [\v!autopunctuation=\v!no]

%D \macros
%D   {mathstyle}
%D
%D If one want to be sure that something is typeset in the
%D appropriate style, \type {\mathstyle} can be used:
%D
%D \starttyping
%D \mathstyle{something}
%D \stoptyping

% \def\mathstyle#1%
%   {\mathchoice
%      {\displaystyle     #1}%
%      {\textstyle        #1}%
%      {\scriptstyle      #1}%
%      {\scriptscriptstyle#1}}
%
% We now have a primitive operation for this. As the
% macro overloads a new primitive introduced in \LUATEX,
% we need to use \type {\normalmathstyle} when we consult
% the current math style.
%
% \let \mathstyle \Ustack % spoils cramped
%
% \let \mathstyle \firstofoneargument
%
% 0 = display
% 1 = crampeddisplay
% 2 = text
% 3 = crampedtext
% 4 = script
% 5 = crampedscript
% 6 = scriptscript
% 7 = crampedscriptscript

\def\uncramped#1%
  {{\ifcase\normalmathstyle
    \or \displaystyle      \or
    \or \textstyle         \or
    \or \scriptstyle       \or
    \or \scriptscriptstyle \fi
    #1}}

\def\cramped#1%
  {{\ifcase\normalmathstyle
    \crampeddisplaystyle      \or \or % 0 -> 1
    \crampedtextstyle         \or \or % 2 -> 3
    \crampedscriptstyle       \or \or % 4 -> 5
    \crampedscriptscriptstyle \fi     % 6 -> 7
    #1}}

\def\triggermathstyle#1% #1 is number
  {\ifcase#1\relax
     \displaystyle             \or
     \crampeddisplaystyle      \or
     \textstyle                \or
     \crampedtextstyle         \or
     \scriptstyle              \or
     \crampedscriptstyle       \or
     \scriptscriptstyle        \or
     \crampedscriptscriptstyle \else
     % error
   \fi}

\def\cramped#1%
  {{\ifcase\normalmathstyle
    \crampeddisplaystyle      \or \or % 0 -> 1
    \crampedtextstyle         \or \or % 2 -> 3
    \crampedscriptstyle       \or \or % 4 -> 5
    \crampedscriptscriptstyle \fi     % 6 -> 7
    #1}}

\def\mathstylefont#1% #1 is number (\normalmathstyle)
  {\ifcase#1\relax
     \textfont         \or
     \textfont         \or
     \textfont         \or
     \textfont         \or
     \scriptfont       \or
     \scriptfont       \or
     \scriptscriptfont \or
     \scriptscriptfont \else
     \textfont
   \fi\zerocount}

%D Something similar can be used in the (re|)|definition
%D of \type {\text}. This version is a variation on the one
%D in the math module (see \type{m-math} and|/|or \type
%D {m-newmat}).

\unexpanded\def\mathtext
  {\mathortext\domathtext\hbox}

\def\domathtext#1%
  {\mathchoice
     {\dodomathtext\displaystyle\textface        {#1}}%
     {\dodomathtext\textstyle   \textface        {#1}}%
     {\dodomathtext\textstyle   \scriptface      {#1}}%
     {\dodomathtext\textstyle   \scriptscriptface{#1}}}

\def\dodomathtext#1#2#3% no \everymath !
 %{\hbox{\everymath{#1}\switchtobodyfont  [#2]#3}} % 15 sec
  {\hbox{\everymath{#1}\setcurrentfontbody{#2}#3}} %  3 sec (no math)

%D Safeguard against redefinitions:

\appendtoks
    \let\_\normalunderscore % is textunderscore or fakeunderscore
\to \everymathematics

%D Because we may overload \type {\text} in other (structuring)
%D macros, we say:

\appendtoks \let\text\mathtext \to \everymathematics

%D The next code is derived from plain \TEX.

\newcount\interdisplaylinepenalty \interdisplaylinepenalty=100

\newif\ifdt@p

\def\displ@y
  {\global\dt@ptrue
   \openup\displayopenupvalue % was \openup\jot
   \everycr
     {\noalign
        {\ifdt@p
           \global\dt@pfalse
           \ifdim\prevdepth>-\thousandpoint
             \vskip-\lineskiplimit
             \vskip\normallineskiplimit
           \fi
         \else
           \penalty\interdisplaylinepenalty
         \fi}}}

\let\normaldispl@y\displ@y

\def\displ@y{\resetdisplaymatheq\normaldispl@y}

\def\m@th{\mathsurround\zeropoint} % obsolete

%D Text in math:

\def\mathortext
  {\ifmmode
     \expandafter\firstoftwoarguments
   \else
     \expandafter\secondoftwoarguments
   \fi}

% \defineactivecharacter _ {\mathortext{_}{\_}} text_text  $a^2$

% force text mode, will be overloaded later

\ifx\text\undefined \let\text\hbox \fi

\def\mathoptext#1{\mathop{\text{#1}}}

\protect \endinput