Stacked fractions
From Why start at x, y, z
A fraction written on multiple levels is often ambiguous, especially when handwritten. For example, \(\frac{10}{\frac{2}{5}}\) and \(\frac{\frac{10}{2}}{5}\) result in 25 and 1, respectively.
Things get even worse when you use the letter \(\Xi\) in this convoluted example[1]:
