texmath-0.6.7: tests/writers/mfrac-07.tex
\frac{\frac{\overset{\phantom{\mathrm{!}}}{{a}}}{{b}} }{\frac{{c}}{{d}} } =\frac{\frac{{a}}{{b}} }{\frac{{c}}{\underset{\phantom{\mathrm{!}}}{{d}}} } \frac{\frac{\overset{\phantom{\mathrm{!}}}{{a}}}{{b}} }{\frac{{c}}{{d}} } =\frac{\frac{{a}}{{b}} }{\frac{{c}}{\underset{\phantom{\mathrm{!}}}{{d}}} }