# Issue With Example of Series Inversion

I am having a problem with the Mathematica InverseSeries command.

Looking at the information page here, we have the following example;

InverseSeries[x^2 + 3 x^4 + O[x]^8]


With output $$\sqrt{x}-\frac{3 x^{3/2}}{2}+\frac{63 x^{5/2}}{8}+O\left(x^{15/2}\right)$$. This works fine for me. They then invert this expression again;

InverseSeries[%]


Which outputs $$x^2+3 x^4+O(x)^8$$, as one would expect. However when I run these commands I simply get;

InverseSeries[x^2+3x^4+O[x]^8]
Sqrt[x]-(3 x^(3/2))/2+(63 x^(5/2))/8+O[x]^(15/2)

InverseSeries[%]
InverseSeries[(x-(3 x^3)/2+(63 x^5)/8)+O[x]^28,x]^2


I don;t have a heap of experience with mathematica, but I have noticed similar behaviour when I have inputted expressions incorrectly. Here thoguh I am literally copy and pasting from the examples webpage.

Any help would be much appreciated, thanks!

• Works fine for me (Windows 10, Mathematica 11.3) - which version are you using? Also, did you try to restart Mathematica to see if it still happens then? – Lukas Lang Oct 6 '19 at 12:40
• I saw a similar problem with v12 on a Mac; however, when I quit the kernel and restarted, it worked as expected except that the order was different. That is, I end up with x^2 + 3x^4 + O[x]^7 – Bob Hanlon Oct 6 '19 at 22:27
• Im on Windows 10, Mathematica 11.1. I have tried restartign and quitting the kernel. I'm currently downloading version 12.0 to see if that helps. – CoffeeCrow Oct 6 '19 at 22:55