LaTeX reader: limits of \mathop{x} and both scripts of \overbrace/\underbrace

src/SharpEquations/Internal/LaTeX/LaTeXReader.cs

@@ -648,6 +648,14 @@ private static string RewriteTeXOnly(string latex)
                     i = afterUnderBase;
                     continue;
                 }
+                if (cw is "overbrace" or "underbrace" && Argument(tex, j) is var (braced, afterBraced) && afterBraced >= 0 &&
+                    Scripts(tex, afterBraced) is var (braceUnder, braceOver, afterBraceScripts) && braceUnder != null && braceOver != null)
+                {
+                    // \overbrace3^a_x: for TeX the brace is an operator with limits, both scripts under and over the whole construct
+                    result.Append(RewriteTeXOnly("\\underset{" + braceUnder + "}{\\overset{" + braceOver + "}{\\" + cw + "{" + braced + "}}}"));
+                    i = afterBraceScripts;
+                    continue;
+                }
                 if (cw == "underset" && Arguments(tex, j, 2) is var (underArguments, afterUnderset) &&
                     new Text(underArguments[1].Trim()) is var overText && overText.Find("\\overset", 0) == 0 &&
                     Arguments(overText, 8, 2) is var (overArguments, afterOverset) && afterOverset == overText.Length)
@@ -718,8 +726,14 @@ private static string RewriteTeXOnly(string latex)
                 }
                 if (cw == "mathop" && BracedArgument(tex, j) is var (operatorText, afterOperator) && afterOperator >= 0)
                 {
-                    // \mathop{\mathrm{argmin}}: an operator name
+                    // \mathop{\mathrm{argmin}}: an operator name; \mathop{x}, of one symbol, a group, which takes the limits
                     var name = operatorText.Trim();
+                    if (Js.Len(name) == 1)
+                    {
+                        result.Append('{').Append(RewriteTeXOnly(name)).Append('}');
+                        i = afterOperator;
+                        continue;
+                    }
                     if (name.StartsWith("\\mathrm{", StringComparison.Ordinal) && name[name.Length - 1] == '}')
                         name = name.Substring(8, name.Length - 9);
                     result.Append(name.All(char.IsLetter) ? "\\operatorname{" + name + "}" : RewriteTeXOnly(operatorText));

tests/SharpEquations.Tests/LaTeX/LaTeXReaderTests.cs

@@ -137,6 +137,12 @@ public class LaTeXReaderTests
         [Arguments(@"\langle a \vert b \rangle", @"\langle a|b\rangle", @"⟨𝑎│𝑏⟩")]
         [Arguments(@"\left. x \right. ", @"x", @"𝑥")]
         [Arguments(@"\mathop{\sum}_i", @"\sum_i", @"∑_𝑖")]
+        [Arguments(@"\mathop{x}\limits_0^1", @"\underset{0}{\overset{1}{x}}", @"𝑥┬0┴1")]
+        [Arguments(@"\underset{0}{\overset{1}{x}}", @"\underset{0}{\overset{1}{x}}", @"𝑥┬0┴1")]
+        [Arguments(@"\overbrace3^a_x", @"\underset{x}{\overset{a}{\overbrace{3}}}", @"⏞3┬𝑥┴𝑎")]
+        [Arguments(@"\underset{x}{\overset{a}{\overbrace{3}}}", @"\underset{x}{\overset{a}{\overbrace{3}}}", @"⏞3┬𝑥┴𝑎")]
+        [Arguments(@"\underbrace{a+b}_n^x+c", @"\underset{n}{\overset{x}{\underbrace{a+b}}}+c", @"⏟(𝑎+𝑏)┬𝑛┴𝑥+𝑐")]
+        [Arguments(@"\underset{n}{\overset{x}{\underbrace{a+b}}}+c", @"\underset{n}{\overset{x}{\underbrace{a+b}}}+c", @"⏟(𝑎+𝑏)┬𝑛┴𝑥+𝑐")]
         [Arguments(@"\xleftarrow{g}", @"\overset{g}{\leftarrow}", @"←┴𝑔")]
         [Arguments(@"\pmod n", @"(\mod\,n)", @"(mod⁡ 𝑛)")]
         [Arguments(@"\hspace*{2cm}x", @"x", @"𝑥")]

tests/SharpEquations.Tests/LaTeX/Latex2MathMLCorpusTests.cs

@@ -198,12 +198,12 @@ private static string Canonical(Equation equation)
 
         // LaTeX and amsmath that the reader does not read yet: an operator name with nothing after it (\lg, \liminf,
         // \injlim, \operatorname*{argmax}_x), which UnicodeMath reads as letters, and the names of amsmath that are two
-        // words (lim inf); \limits after \mathop; both scripts of \overbrace and \underbrace; \middle between empty
-        // delimiters and bars with nothing between them (|\,|); \newenvironment and ## in a macro
+        // words (lim inf); \middle between empty delimiters and bars with nothing between them (|\,|); \newenvironment
+        // and ## in a macro
         private static readonly HashSet<string> NotReadYet = new HashSet<string>
         {
             "lg", "liminf", "limsup", "injlim", "projlim", "varinjlim", "operatornamewithlimits", "operatorname-star",
-            "issue-125-4-limits", "overbrace-c", "underbrace-c", "middle", "spaces",
+            "middle", "spaces",
             "newenvironment-multi-node", "newcommand-escaped-hash",
         };