Sat Nov 18 17:07:58 EST 2017

Closures vs. build instructions

So I would want the collection of .nix files that lead up to a
particluar closure.  In practice, it is likely sufficient to:

- start with a well-defined root (e.g. 17.03 or 17.09)
- keep a copy of that root as nixpkgs
- add modified packages on top of that