### Typo in Sagemanifolds worksheet ?

Sorry to bother the group but I don't know how to report a technical (but inconsequential) typo in Kerr_Schild.ipynb
Where should I report it?
After In[33] or so, "Check of the Identity"

```
\frac{x^2 + y^2}{r^2 + a^2} + \frac{z^2}{r^2} = 1
```

Should be:

```
\frac{x^2 + y^2}{R^2 + a^2} + \frac{z^2}{R^2} = 1
```

It seems to be too trivial for a 'Ticket' on the Sagemanifolds forum. I am just reading the program in detail; checking my understanding.