metamath · digama0 · Sep 24, 2023 · Aug 20, 2023 · Aug 20, 2023 · Aug 20, 2023
diff --git a/src/mmhlpa.c b/src/mmhlpa.c
@@ -635,7 +635,9 @@ H("interpreted by / SYMBOLS, / LABELS, and / BIB_REFS respectively, escape");
 H("them with \"``\", \"~~\", and \"[[\" in the input file.  Literal \"`\"");
 H("must always be escaped even if / SYMBOLS is omitted, because the");
 H("algorithm will still use \"`...`\" to avoid interpreting special");
-H("characters in math symbols.");
+H("characters in math symbols.  Similarly, use a double underscore to");
+H("display one underscore \"_\" and not trigger an italic font or");
+H("subscripts.");
 H("");
 }
 

diff --git a/src/mmwtex.c b/src/mmwtex.c
@@ -1963,6 +1963,27 @@ flag printTexComment(vstring commentPtr, flag htmlCenterFlag,
       if (!strcmp(mid(cmt, pos2 + 2, 2), "mm")) {
         continue;
       }
+      // Double-underscore handling: double-underscores are "escaped
+      // underscores", so replace a double-underscore with a single
+      // underscore and do not modify italic or subscript.
+      if (cmt[pos1] == '_') {
+            if (g_htmlFlag) {  // HTML
+              let(&cmt, cat(left(cmt, pos1), // Skip (delete) "_"
+                  right(cmt, pos1 + 2), NULL));
+              let(&cmtMasked, cat(left(cmtMasked, pos1), // Skip (delete) "_"
+                  right(cmtMasked, pos1 + 2), NULL));
+              pos1 ++; // Adjust for 1 extra char '_'
+            } else {  // LaTeX
+              let(&cmt, cat(left(cmt, pos1 - 1),  // Skip (delete) "_"
+                  "\\texttt{\\_}",
+                  right(cmt, pos1 + 2), NULL));
+              let(&cmtMasked, cat(left(cmtMasked, pos1 - 1),  // Skip (delete) "_"
+                  "\\texttt{\\_}",
+                  right(cmtMasked, pos1 + 2), NULL));
+              pos1 = pos1 + 11; // Adjust for 11 extra chars "\texttt{\_}"
+            }
+        continue;
+      } // End of double-underscore handling
 
       // Opening "_" must be <whitespace>_<alphanum> for <I> tag
       if (pos1 > 1) {

diff --git a/tests/underscores.expected b/tests/underscores.expected
@@ -0,0 +1,105 @@
+MM> READ "underscores.mm"
+Reading source file "underscores.mm"... 193 bytes
+193 bytes were read into the source buffer.
+The source has 2 statements; 1 are $a and 0 are $p.
+SET EMPTY_SUBSTITUTION was turned ON (allowed) for this database.
+No errors were found.  However, proofs were not checked.  Type VERIFY PROOF *
+if you want to check them.
+MM> Continuous scrolling is now in effect.
+MM> Creating HTML file "b.html"...
+Reading definitions from $t statement of underscores.mm...
+1 typesetting statements were read from "underscores.mm".
+MM> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
+    "http://www.w3.org/TR/html4/loose.dtd">
+<HTML LANG="EN-US">
+<HEAD>
+<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
+<META NAME="viewport" CONTENT="width=device-width, initial-scale=1.0">
+<STYLE TYPE="text/css">
+<!--
+img { margin-bottom: -4px }
+.r { font-family: "Arial Narrow";
+     font-size: x-small;
+   }
+.i { font-family: "Arial Narrow";
+     font-size: x-small;
+     color: gray;
+   }
+-->
+</STYLE>
+
+<TITLE>b - Metamath Test Page</TITLE>
+<LINK REL="shortcut icon" HREF="favicon.ico" TYPE="image/x-icon">
+</HEAD>
+<BODY BGCOLOR="#FFFFFF">
+<TABLE BORDER=0 CELLSPACING=0 CELLPADDING=0 WIDTH="100%">
+  <TR>
+    <TD ALIGN=LEFT VALIGN=TOP WIDTH="25%"><A HREF=
+    "mmset.html"><IMG SRC="mm.gif"
+      BORDER=0
+      ALT="MTP Home"
+      TITLE="MTP Home"
+      HEIGHT=32 WIDTH=32 ALIGN=TOP STYLE="margin-bottom:0px"></A>
+    </TD>
+    <TD ALIGN=CENTER COLSPAN=2 VALIGN=TOP><FONT SIZE="+3" COLOR="#006633"><B>
+Metamath Test Page
+      </B></FONT></TD>
+    <TD ALIGN=RIGHT VALIGN=TOP WIDTH="25%">
+      <FONT SIZE=-1 FACE=sans-serif>
+      <A HREF="b.html">
+      &lt; Wrap</A>&nbsp;&nbsp;
+      <A HREF="b.html">Wrap &gt;</A>
+      </FONT><FONT FACE=sans-serif SIZE=-2>
+      <BR><A HREF="mmtheorems1.html#b">Nearby theorems</A>
+      </FONT>
+    </TD>
+  </TR>
+  <TR>
+    <TD COLSPAN=2 ALIGN=LEFT VALIGN=TOP><FONT SIZE=-2
+      FACE=sans-serif>
+      <A HREF="../mm.html">Mirrors</A>&nbsp; &gt;
+      &nbsp;<A HREF="../index.html">Home</A>&nbsp; &gt;
+      &nbsp;<A HREF="mmset.html">MTP Home</A>&nbsp; &gt;
+      &nbsp;<A HREF="mmtheorems.html">Th. List</A>&nbsp; &gt;
+      &nbsp;b
+      </FONT>
+    </TD>
+    <TD COLSPAN=2 ALIGN=RIGHT VALIGN=TOP>
+      <FONT SIZE=-2 FACE=sans-serif>
+
+      </FONT>
+    </TD>
+  </TR>
+</TABLE>
+<HR NOSHADE SIZE=1>
+<CENTER><B><FONT SIZE="+1">Syntax Definition <FONT
+COLOR="#006633">b</FONT></FONT></B>&nbsp;<SPAN CLASS=r
+STYLE="color:#FB0000">1</SPAN></CENTER>
+<CENTER><TABLE><TR><TD ALIGN=LEFT><B>Description: </B>This is <I>italic</I> and
+the command &quot;MM-PA&gt; MINIMIZE_WITH *&quot; and a
+     sub<SUB><FONT SIZE="-1">script</FONT></SUB>.</TD></TR></TABLE></CENTER>
+
+<CENTER><TABLE BORDER CELLSPACING=0 BGCOLOR="#EEFFFA"
+SUMMARY="Assertion">
+<CAPTION><B>Assertion</B></CAPTION>
+<TR><TH>Ref
+</TH><TH>Expression</TH></TR>
+<TR ALIGN=LEFT><TD><FONT COLOR="#006633"><B>b</B></FONT></TD><TD>
+<SPAN >a</SPAN></TD></TR>
+</TABLE></CENTER>
+
+
+<HR NOSHADE SIZE=1>
+</TABLE></CENTER>
+<TABLE BORDER=0 WIDTH="100%">
+<TR><TD WIDTH="25%">&nbsp;</TD>
+<TD ALIGN=CENTER VALIGN=BOTTOM>
+<FONT SIZE=-2 FACE=sans-serif>
+Copyright terms:
+<A HREF="../copyright.html#pd">Public domain</A>
+</FONT></TD><TD ALIGN=RIGHT VALIGN=BOTTOM WIDTH="25%">
+<FONT SIZE=-2 FACE=sans-serif>
+<A HREF="http://validator.w3.org/check?uri=referer">
+W3C validator</A>
+</FONT></TD></TR></TABLE>
+</BODY></HTML>
diff --git a/tests/underscores.in b/tests/underscores.in
@@ -0,0 +1,2 @@
+show statement b/alt_html
+"cat b.html"
diff --git a/tests/underscores.mm b/tests/underscores.mm
@@ -0,0 +1,10 @@
+  $c a $.
+
+  $( This is _italic_ and the command "MM-PA> MINIMIZE__WITH *" and a
+     sub_script. $)
+  b $a a $.
+
+$( $t
+ htmldef "a" as "a";
+  althtmldef "a" as "a";
+   latexdef "a" as "a"; $)