munder-03.tex

\underset{\genfrac{}{}{0.0mm}{}{\mathrm{first\ under\ script}}{\mathrm{second\ one}} }{\mathrm{BASE}}=\underset{\phantom{\mathrm{fail}}}{\underset{\genfrac{}{}{0.0mm}{}{\mathrm{first\ under\ script}}{\mathrm{second\ one}} }{\mathrm{BASE}}}