Compositional inverse of multivariate power series

[Peter Luschny]

The compositional inverse (with respect to x) of 

    y(t, x) = x - t*(exp(x) - 1)

is

    1/(1-t)*y + t/(1-t)^3*y^2/2! + (t+2*t^2)/(1-t)^5*y^3/3! + (t+8*t^2+6*t^3)/(1-t)^7*y^4/4! + ...

Apparently multivariate power series rings do not know how 

to reverse a series.     

Perhaps there is a workaround?

Thanks!

[Dima Pasechnik]

one can try to see if working with univariate series over R(t) will
give the needed inverse.


> Thanks!
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