I've integrated this into the fixes branch and informed Carlos.

List of potentially affected domains (those that use :constants):

airport
openstacks-opt08-strips
openstacks-sat08-strips
parcprinter-08-strips
pathways
pathways-noneg
pipesworld-notankage
pipesworld-tankage
psr-large
psr-middle
schedule
woodworking-opt08-strips
woodworking-sat08-strips

OK, fix merged and pushed.
Michael and Erez, thanks for reporting this, and Gabi, thanks for fixing! :-)

Now we need to check which domains are affected, integrate this into the IPC
fixes branch, notify Carlos, and notify everyone else who's working with our
translator.

Yes, that's guaranteed because the equivalence classes are represented as sets.
The elements are variables and constants represented as string.

Thanks, Gabi!

In the case that there are two element in "constants" in that method, is it
actually guaranteed that they are two *different* constnats (i.e., not two
copies of the same one)?

This was a bug in the invariant synthesis that could only occur when constants
were used in the action specification.

OK, attached a much simplified test case (still big, but much much easier to
understand). With this test case, the old translator gives a solution of length
39, while the new one completely explores the state space up to depth 69,
failing to find a solution.

The new encoding (as per test.groups) appears to claim that at most one airplane
can be facing north at a time. If I interpret the plan from the old encoding
correctly, this is wrong, so this might be the source of the problem.

Passing over to Gabi.

PS: Gabi: Using invariant_finder.py as a top-level script seems to be broken.

OK, all confirmed. Will look into it.

I used the version in the SVN trunk.

Adding Gabi. I can confirm the length-75 solution.
Erez, which version of the translator did you use for the "old" result?

I should not this was found by Michael.

In airport-p09, using the new translator and then astar with blind search finds 
a solution of length 75.
Using the old translator (and the new preprocessor and search) finds a solution 
of length 71.
Both solution are validated by VAL.