The key to solving complex design 
problems is to break them down into 
smaller pieces. 
Now, the recipes already do that of 
course. 
The data recipe breaks data design down 
into individual steps. 
The function recipe does the same, and 
so, does the world recipe. 
But sometimes we need more decomposition 
than that. 
Sometimes we need to break a data 
representation into multiple types, or a 
function design in the multiple 
functions. 
Now, we've seen a couple examples of that 
already of course. 
Whenever we have the reference rule, then 
we end up with a natural helper function. 
And the world's recipe also breaks the 
design down into multiple handlers. 
But this week, we're going to look at 
more examples of how we break types and 
functions down into multiple types and 
multiple functions. 
The week is broken into two parts. 
In the first part, we're going to look at 
rules for helper functions operating on 
the kinds of data we've already seen. 
In the second part, we're going to 
introduce a new kind of arbitrary size 
data. 
And that kind of data definition itself 
automatically introduces helpers into the 
functions that operate on the data.