HP Prime: built-in inverse function of erf?

[Albert Chan]

Examples were run on HP Prime emulator, 2.1.14181 (2018 10 16)
We don't really need solver for this. Plain newton's method work well.

> a := 0.8-0.2i
> Ans - (f:=erf(Ans)-a) / (2/sqrt(pi)*exp(-Ans^2))

0.817846322321-0.344502692613*i
0.800996592256-0.340824015653*i
0.801172956998-0.341012320073*i
0.801172930852-0.341012371793*i

Or, speed up with Halley's method

> a
> Ans - (f:=erf(Ans)-a) / (2/sqrt(pi)*exp(-Ans^2)+Ans*f)

0.800849610571-0.342519806279*i
0.801172932494-0.34101237069*i
0.801172930852-0.341012371793*i