FLiP package organization

FLiP 1.2 organizes the modules (.py source files) into Python packages
(directories that contain an __init__.py file).  Previous versions did
not use packages.  Packages provide several advantages.  They make it
convenient to use FLiP from outside its own development directories,
and to add case studies and define logics outside those directories.
This makes it convenient to install FLiP in the usual installation
directories (site-packages or dist-packages or ...), rather then run
it right out of the unpacked distribution.  Packages (along with
installation) remove or very much reduce the need to manipulate
PYTHONPATH in order to use FLiP.  Packages also encourage simpler or
clearer module names: session.py and contradiction.py instead of
poset_session.py and contra_test.py.

If you have installed FLiP you can start an interactive proof session
using first-older logic (fol) in any directory with this command:
 
 python -i -m flip.logic.fol_session

or, name another session module for another logic. This works if the
directory that contains the flip package is on PYTHONPATH.  Normally,
installing FLiP achieves this.  See www/download.html.

Of course, you can still do it the old way that doesn't use packages.
For that, you must run from the FLiP-1.2/flip/logic directory in the
unpacked distribution and type this command:

 python -i fol_session.py

Most of the FLiP software, including all the logics developed so far,
is in the flip.logic package and the tests for all of these logics
are in the flip.test package.  It is recommended that from now on,
each new logic get its own package.  As an example, this version
includes a flip.poset package for the logic of Partially Ordered Sets
from Kaye chapter 4.  To start an interactive proof session in this
logic:

 python -i -m flip.poset.session

Also, this package contains its own test package flip.poset.test.  
See the README.txt files in those packages for details.

This is the directory organization of FLiP-1.2.  Each directory that
contains an __init__.py module is a package.  All of the __init__.py
modules are empty.

  FLiP-1.2/
    README.txt
    setup.py
    ...
    bin/
      plogdiff
      ...
    notes/
      packages.txt
      ...
    www/
      download.html
      ...
    flip/
      __init__.py
      logic/
         __init__.py
         nd.py
         formula.py
         fol.py
         fol_session.py
         ...
       test/
         __init__.py
         fol_test.py
         fol_test.ref
         ...
       grail/
         __init__.py
         witch.py
         ...
       poset/
         __init__.py
         poset.py
         session.py
         test/
           __init__.py
           exercises.py
           ...