Add paper data layout

This patchset adds contents to the section "Data layout" which describes the internal structure of the set in more detail.
This sentence is syntactically wrong. It could also be embedded in the formula, which would be much more readable, as if you read the formula, you want to see something like this definition.

I would change the formula to:

```latex
s(A) < s(B) \Rightarrow e(b) \subseteq e(a_1) \ equiv \lnot e(b) \subseteq e(a_2), a_n \elementof A, b \elementof B
```

or something similar.

--- 

I would also change the last part of the function (`e(b) \subseteq e(a_1) \equiv \lnot e(b) \subseteq e(a_2)`) to something like

```latex
e(b) \subseteq e(a_1) \or \lnot e(b) \subseteq e(a_2)
```
(using an XOR)
As `e(b)` is _either_ a subset or equal to `a_1` _xor_ `a_2`, am I right?

I would contribute patches if you want me to change this,