## Special functions

I just find a bug looking at my coefficients (issue #32 (closed)). I used the spherical hankel function of the first kind instead of the second kind. I will open a new branch to implement the second kind and I would suggest the following name-changes:

for the spherical Besselfunctions of the first kind:

```
jn_1
d1_jn_1
d2_jn_1
...
```

for the spherical Besselfunctions of the second kind:

```
jn_2
d1_jn_2
d2_jn_2
...
```

for the spherical hankel function of the first kind:

```
hn_1
d1_hn_1
d2_hn_2
...
```

for the spherical hankel function of the second kind:

```
hn_2
d1_hn_2
d2_hn_2
...
```

Alternatively we could also define the spherical besselfunction of the first kind like that:

`def jn_1(cls, n: int, z: complex, d: int) `

with `d `

being the derivative. we could then make a simple switch / if-else block to select the derivative.
I am not sure, if this is already done in the funciton `adaptive_derivative`

WHat do you think?