hide fricasmath environment from HyperDoc

src/doc/htex/ug04.htex

@@ -363,6 +363,7 @@ matrix [[i*x^i + j*\%i*y^j for i in 1..2] for j in 3..4]
 \end{MATRIX}%
 \end{fricasmath}
 \end{verbatim}
+\begin{texonly}
 With the definition of the fricasmath environment as defined in
 fricasmath.sty this formats as
 \begin{fricasmath}{1}
@@ -373,6 +374,7 @@ fricasmath.sty this formats as
 \ImaginaryI \TIMES \SUPER{\SYMBOL{y}}{4}+2\TIMES \SUPER{\SYMBOL{x}}{2}%
 \end{MATRIX}%
 \end{fricasmath}
+\end{texonly}
 To turn \TeX{} output formatting off, issue
 \spadsys{)set output tex off}.
 The \LaTeX{} macros in the output generated by \Language{}