More space transform functions, plus now I know how to spell "apply".
Space is more organized now, and has a 'contains' primitive.
Now, instead of fillings two corridors, one with air and one with stone, we fill once and just place smooth-stone-brick in the bottom most blocks.
Joining up the spaces makes floors nice and smooth, but not always connected up. Not so good in the nether, but I call it progress.