I want to try asymptotic output tracking, but with inequality.

There is a differential equation:

$frac{dx}{dt}=frac{d}{dx}(-x^4)$

With output $y=frac{d}{dx}(-x^4)$,

The output should strive for $0$, i.e. $r_1=0$. Wherein $-1<x<1$.

```
(***)
Clear("Derivative")
ClearAll("Global`*")
f = -x(t)^4
asys = AffineStateSpaceModel({x'(t) - D(f, x(t)) == u(t)}, {{x(t),
1.25}}, {u(t)}, {D(f, x(t))}, t) // Simplify
pars1 = {Subscript(r, 1) -> 0, Subscript(p, 1) -> -10}
fb = AsymptoticOutputTracker(
asys, {Subscript(r, 1)}, {Subscript(p, 1)}) // Simplify
```

I do not know whether it is possible to solve this task and how to set the required inequality.

I will be glad to any advice and help.