Oh, as soon as I submitted the comment, I think I see the answer. (it's always that way...)

You need to be able to say

```js
graph.addLazy('lazylog2', function (x, y) { console.log(x, y); return true }, ['x'])
    .builds('y')
```
and not have the 'y' fire unless the thunk from lazylog2 gets executed. Is that right?