How to place an inscription under a symbol in TEX?

Question

TeX

On the screen they are highlighted in yellow, here you need to place signatures under them

Answer 1

Try something like
for the first formula, for the second
For the third also \stackrel
In the preamble, write \usepackage{stackrel}

Answer 2

\stackrel did not work, probably there is no such plugin (or rights), but the search for "TEX stackrel" found {x \atop y} b - it suits me.
thanks for pointing the way.