sympy/sympy — pull request #2830 by SDB1323 (2014-01-25 19:50:12+00:00)
Title: Fixed PropKB Ask. Added function to check validity.

1. Added function to check for validity of propositional sentences
2. Fixed bug where all queries on an empty KB would return False
3. Fixed PropKB Ask function to correctly give the logical entailment
4. Added Tests for the above