Suppose that some knowledge base contains various propositional-logic sentences that utilize symbols a, b, c, d (connected with various connectives). there are only two cases when the knowledge base is false:
- first case: when a is true, b is true, c is true, d is true.
- second case: when a is true, b is false, c is true, d is false.
in all other cases, the knowledge base is true. write a conjunctive normal form (cnf) for the knowledge base.