Still left to do
================

- consider reducing the size of the lists of conflicts, e.g., by making
  them unique via a red-black tree

- handle Provides:

- sort prerequisites such that they can be installed in the specified order

- consider Architecture:

  Update: we parse and record it now but don't use it yet.

- what to do with explicit and implicit replacement ?

- if we can't resolve the prerequisites, give at least a hint of what one
  can do to improve the situation

- check database for internal consistency

  Update: added detection of cyclic dependencies (in progress)

  Update: added test for QPKG_ADDING cleanup bug

- implement keyword search

- consider also supporting the similar but not identical (parent ?) format
  of /var/lib/dpkg/status and /var/lib/apt/lists/*Packages


Done
====

- optimize the search trees. Right now, we have 81812 calls to make_id
  for 14601 packages, resulting in 7420560 calls to comp_id.

  There can be at most 2 new identifiers per package (package name and
  version), so a perfectly balanced tree should have a depth of no more
  than 14. If we assume that each call to make_id searches to the bottom,
  we'd get 1145368 calls to comp_id, about 15% of the current number.

  So the tree is clearly degenerated.

  Update: after switching to red-black trees, we get only 1497604 calls
  to comp_id. This is 130% of the "good case" estimate above. Insertion
  of a new node is currently done with two lookups, so we'll get rid of
  some more lookups after further optimization.

  Update: after merging the two lookups per new node into one, we're at
  1172642 calls to comp_id, or 102% of the predicted "good case".

- if there are multiple choices, try to prefer more recent versions

- check whether introducing a new package would cause a conflict

  Update: conflicts among the packages considered for installation are now
  checked.

- compile the list of conflicts of installed packages