More clear definition and derivation for CLP derivation Eq1 & 2

[tree-pi]

For this document, I suggest the edit as follows:

Start with the fixed-product formula:

$$ Eqn 1: X*Y = K $$

Now that assuming swapping $x$ for the amount of $y$, so that $X*Y=(X+x)(Y-y)$. We can then derive the raw "XYK" output:

$$ Eqn 2: y= \frac{xY}{x+X} $$