For references on syntax and semantics of propositional and perdicate logic and natural dedeuction, see:
For references on syntax and semantics of propositional and perdicate logic and exercises, see:
Pandora: Proof Assistant for Natural Deduction. Please visit the guideline page for instructions on how to run Pandora remotely.
PBL: A Python Boolean library for parsing and manipulating boolean formulae.
PBL online: Converting propositional logic formulas to CNF.