#let s = state("hey", "a")
#let double(it) = 2 * it

#s.update(double)
#s.update(double)
$ 2 + 3 $
#s.update(double)

Is: #s.display(),
Was: #locate(location => {
  let it = query(math.equation, location).first()
  s.at(it.location())
}).