Chapter 55
amsthm.sty

<..amsthm.4ht..>
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % amsthm.4ht                            2014-07-12-22:36 %
 % Copyright (C) 1997--2009       Eitan M. Gurari         %
 <.TeX4ht copyright.>
 
 <.body of amsthm.sty.>
 <.theorem in amsthm.sty.>
 \Hinput{amsthm}
 \endinput
 -_-_-

<..body of amsthm.sty..>
 <.qed symbol.>
 -_-_-

<..qed symbol..>
 \def\qed:sym{%
   \leavevmode\Picture+[Q.E.D.]{}\o:qedsymbol:\EndPicture
   \SavePicture\qed:sym[Q.E.D.] }
 \def\:temp{\qed:sym }
 \MathSymbol\mathop{qedsymbol}
 -_-_-

<..shared ams thm/cls..>
 \ifx \deferred@thm@head\:UnDef\else
    \expandafter\dth@everypar\expandafter{%
      \the\dth@everypar
      \edef\:temp{\the\ht:everypar}\ifx \:temp\empty
         \ht:everypar{\HtmlPar}\ShowPar
      \fi
    }%
    <.revised begintheorem.>
 \fi
 -_-_-

<..revised begintheorem..>
 \def\deferred@thm@head#1{%
   \if@inlabel \indent \par \fi  eject a section head if one is pending
   \if@nobreak
     \adjust@parskip@nobreak
   \else
     \addpenalty\@beginparpenalty
     \addvspace\@topsep
     \addvspace{-\parskip}%
   \fi
   \global\@inlabeltrue
   \ht:everypar\dth@everypar
   \let\sv:newtheorem=\b:newtheorem \let\b:newtheorem=\empty
   \item[\normalfont#1]%
   \let\b:newtheorem=\sv:newtheorem \b:newtheorem \ignorespaces
 }
 -_-_-

The old version of amsthm used ‘\item[\normalfont#1]’ instead of ‘\sbox\@labels{\normalfont#1}’–it is preferable for tex4ht, in case the lemma starts with something like ‘\begin{equation}’.

The following code is for the cases that the \refstercounter is ignored in \@thm.

<..theorem in amsthm.sty..>
 \def\:temp{\ShowRefstepAnchor\o:@begintheorem:}
 \HLet\@begintheorem=\:temp
 <.shared ams thm/cls.>
 -_-_-

<..shared ams thm/cls..>+
 \def\:temp#1{%
    \def\:temp{#1}%
    \edef\:temp{\expandafter\eorem:syle  \meaning\:temp<.par del.>}%
    \expandafter\let\expandafter\@tmp:sv\csname th@\:temp\endcsname
    \def\:tempa##1{%
       \expandafter\append:def\csname th@##1\endcsname{%
          \expandafter\let\csname th@##1\endcsname=\@tmp:sv
          \let\thm:headnl=\thmheadnl
          \pend:def\thmheadnl{\let\thmheadnl\thm:headnl \b:newtheorem}%
          \append:def\thmheadnl{\expandafter
              \ht:everypar\expandafter{\the\ht:everypar
              \ht:everypar{\HtmlPar}}}}}%
    \expandafter\:tempa\expandafter{\:temp}%
    \let\sv:trivlist=\trivlist
    \def\trivlist{\let\trivlist\sv:trivlist \let\sv:trivlist\:unDef
       \a:newtheorem \trivlist}%
    \aftergroup\c:newtheorem
    \:thm{#1}}
 \HLet\@thm\:temp
 \HRestore\@endtheorem
 -_-_-

The @thm appends its setting to the hook of theoremstyle:

<..shared ams thm/cls..>+
 \bgroup
 \def\bgroup{\catcode‘\\=0 \catcode‘\t=11 }
 \catcode‘\/=0
 \catcode‘\@=12
 \catcode‘\h=12
 \catcode‘\\=12
 /catcode‘/t=12
 /edef~{/def/noexpand/eorem:syle##1\th@##2 <.par del.>{##2}}
 /bgroup
 \expandafter\egroup ~
 -_-_-

<..shared ams thm/cls..>+
 \long\def\:temp[#1]{\par\a:proof
     \csname o:\string\proof :\endcsname[#1]\b:proof}
 \expandafter\HLet\csname \string\proof \endcsname=\:temp
 \append:def\endproof{\c:proof}
 \NewConfigure{proof}{3}
 -_-_-