Tests from the MathML torture test

(\binom{n}{k / 2})

\iint_{D} d x d y

{\underset{\underset{k + ℓ elements}{⏟}}{\overset{\overset{k a's}{⏞}}{a, ..., a}, \overset{\overset{ℓ b's}{⏞}}{b, ..., b}}}

\sum_{i = 1}^{p} \sum_{j = 1}^{q} \sum_{k = 1}^{r} a_{i j} b_{j k} c_{k i}