simplify inverse_erf(erf(x))

I've found here:
http://mathworld.wolfram.com/InverseErf.html

[image: erf^(-1)(erf(x))][image: =][image: x,]
(2)

with the identity holding for [image: x in R]

But:

(%i10) declare(x, real);

(%o10)                               done
(%i11) declare(y, real);
(%o11)                               done
(%i12) solve(erf(x) = erf(y), x);
(%o12)                     [x = inverse_erf(erf(y))]


Is this a lack of knowlege on maxima's part?
Is this something that should be changed?
Where would I add a failing unit test?
   Feel free to just point me to a similar pull request if you like.