Isomer tools

You will write three small tools that help you sort and count isomers.

The idea. The degrees of unsaturation of $\text{C}_c\text{H}_h\text{N}_n$ with x halogens are $\dfrac{2c + 2 + n - h - x}{2}$. A molecule with k different stereocentres has at most $2^k$ stereoisomers. An isomer is described by three things: its carbon skeleton, its functional group and the position of that group.

Your tasks.

1. In dbe, return the degrees of unsaturation.
2. In stereo_max, return the largest number of stereoisomers for k different stereocentres.
3. In kind, compare two isomers. Return "functional" if the groups differ, else "chain" if the skeletons differ, else "position" if the positions differ, else "same".