HP Prime: built-in inverse function of erf?

[Gil]

"I think erf inverse function is defined only for real x within ±1, otherwise we get infinite solutions."

Not quite so as I understood from Wikipedia, in article Error Function, Properties for Abs (z=a+ib) < 1 :

The inverse error function is usually defined with domain (−1,1), and it is restricted to this domain in many computer algebra systems. However, it can be extended to the disk |z| < 1 of the complex plane, using the Maclaurin series[9]

Then
Inv
ERF

(
(.8,-.2)
)
—>(.801172930851,-.341012371796)

And ERF

(
(.801172930851,-.341012371796)
)
—> (.799999999998,-.200000000002)

Or
Inv
ERF

(
(0.,.85)
) —>
(0.,.649264402037

And ERF

(
(0.,.649264402037)
)
—> (0.,.849999999995)

It's what I developed for the HP50G in the directory program ERROR.9f for the error functions.