Propagation technique: Encapsulation

[emgrasmeder]

Encapsulation works in the following way:

1. Select a tree (with probability proportional to fitness)
2. Choose random point between depth(0) and depth(N)
3. Using that point as a root node, give the subsequent subtree a name and add the named function to the list of usable functions.

Note: Koza suggests making a named function which takes no arguments, but it would also be possible to "destructure" the function, which would allow it to experience sexual crossover / asexual mutation in future generations.