pdflatex crashes when Latex code includes \unicode{f818} and \unicode{f817} and how to handle it

Question

I do not know if the Latex code (which is auto-generated is invalid) or if pdflatex is supposed to be able to handle this code, but I need to find the correct package. I looked at this entering-unicode-characters-in-latex and added the package mentioned there. But still get the error. May be I need to define a macro? Do I need to add a smart \DeclareUnicodeCharacter to handle this? Is there a way to use this \DeclareUnicodeCharacter to make these unicodes below which are causing the problem to be just a single white space so that pdflatex and latex can process the file?

Mathematica generates Latex code for one of its expression which uses special Mathematical symbols (small dot above and below letters) as shown in this link

Here is a screen shot from my notebook showing the Latex code generated

When I use this Latex code in my document, pdflatex.exe actually crashed (MikTex) and also texlive on Linux gave the error:

(/usr/local/texlive/2014/texmf-dist/tex/latex/amsfonts/umsa.fd)
(/usr/local/texlive/2014/texmf-dist/tex/latex/amsfonts/umsb.fd)
! Undefined control sequence.
l.11 ...to \text{DifferentialRoot}\left(\{\unicode
                                                  {f818},\unicode{f817}\}
? 

The code generated is complicated and I can't edit it by hand, else I will break the Latex code generated if I start moving parts around (I also need to run this many times, so need a one time fix)

Here is a MWE on one actual case. I have many such cases, so looking for a macro I can put at top of the Latex document that solves all these \unicode problems. A solution that removes all those unicodes is just fine as well. The symbols do not have to have those dots above or below, but this is how Mathematica generates them. But for the pdf file, I do not need them really.

\documentclass[12pt]{article}
\usepackage{amsmath,mathtools}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[mathletters]{ucs}
\usepackage[utf8]{inputenc} 
\begin{document}

$\left\{\left\{y(x)\to \text{DifferentialRoot}\left(\{\unicode{f818},
  \unicode{f817}\}
  \unicode{f4a1}\left\{\left(a^2 \unicode{f817}^3+a\right) 
  \unicode{f818}(\unicode{f817})+\left(2 \unicode{f817}^3 a-1\right) 
  \unicode{f818}'(\unicode{f817})+\unicode{f817} 
  \unicode{f818}''(\unicode{f817})=0,
  \unicode{f818}(1)=c_1,\unicode{f818}'(1)=c_2\right\}\right)(x)\right\}\right\}$

\end{document} 

Answer 1

U+F817, U+F818 and U+F4A1 point to the private use area, so it's impossible to say what they should produce, because it's font dependent.

Looking at your picture, the correspondence seems to be

• U+F817 is x
• U+F818 is y
• U+F4A1 is ,

So you can do

\makeatletter
\newcommand{\unicode}[1]{\@nameuse{unicode@#1}}
\newcommand{\unidef}[2]{\@namedef{unicode@#1}{#2}}
\makeatother

\unidef{f817}{x}
\unidef{f818}{y}
\unidef{f4a1}{,}

Complete code:

\documentclass[12pt]{article}
\usepackage{amsmath,mathtools}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[utf8]{inputenc}

\makeatletter
\newcommand{\unicode}[1]{\@nameuse{unicode@#1}}
\newcommand{\unidef}[2]{\@namedef{unicode@#1}{#2}}
\makeatother

\unidef{f817}{x}
\unidef{f818}{y}
\unidef{f4a1}{,}

\begin{document}

$\left\{\left\{y(x)\to \text{DifferentialRoot}\left(\{\unicode{f818},
  \unicode{f817}\}
  \unicode{f4a1}\left\{\left(a^2 \unicode{f817}^3+a\right)
  \unicode{f818}(\unicode{f817})+\left(2 \unicode{f817}^3 a-1\right)
  \unicode{f818}'(\unicode{f817})+\unicode{f817}
  \unicode{f818}''(\unicode{f817})=0,
  \unicode{f818}(1)=c_1,\unicode{f818}'(1)=c_2\right\}\right)(x)\right\}\right\}$

\end{document}

I can show only the start, as the formula is unbreakable due to the wrong usage of \left and \right. Whoever wrote the LaTeX code generator doesn't seem to know much about TeX.

Here is the typeset result after removing all \left and \right:

Answer 2

You can add the following code before automatic generated text:

\def\unicode#1{\csname U+#1\endcsname}
\def\unidef#1{\expandafter\def\csname U+#1\endcsname}

\unidef{f818}{{\bdot{\dot y}}}
\unidef{f817}{{\bdot{\dot x}}}
\unidef{f4a1}{,}

\def\bdot#1{\vtop{\offinterlineskip
   \halign{\hfil##\hfil\cr$#1\vphantom y$\cr\noalign{\vskip1pt}.\cr}}}

% the text generated by Mathematica follows:

\documentclass[12pt]{article} 
\usepackage{amsmath,mathtools}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[mathletters]{ucs}
\usepackage[utf8]{inputenc}
\begin{document}

$\left\{\left\{y(x)\to \text{DifferentialRoot}\left(\{\unicode{f818},
  \unicode{f817}\}
  \unicode{f4a1}\left\{\left(a^2 \unicode{f817}^3+a\right) 
  \unicode{f818}(\unicode{f817})+\left(2 \unicode{f817}^3 a-1\right) 
  \unicode{f818}'(\unicode{f817})+\unicode{f817} 
  \unicode{f818}''(\unicode{f817})=0,
  \unicode{f818}(1)=c_1,\unicode{f818}'(1)=c_2\right\}\right)(x)\right\}\right\

\end{document}

I mean that you need to print dot above and below of x, y, thus \bdot is defined.