BDD nondeterminism in a very specific case

[Joachim Jansen]

Running the attached file multiple times results in two possible grounding sizes

groundsize&&71457

and

groundsize&&73366

The reason for this is believed to be in the BDD estimators.

For some reason, when approxdefs are not used (remove the line stdoptions.approxdef="cheap"), this nondeterminism does not occur.

Since nondeterminism is not preferred, this behaviour should be removed.