In computational complexity theory, a problem is NP-complete when: Cook and Levin proved that each easy-to-verify problem can be solved as fast as SAT, which is hence NP-complete. While it is easy to verify whether a given assignment renders the formula true, no essentially faster method to find a satisfying assignment is known than to try all assignments in succession. The Boolean satisfiability problem (SAT) asks to determine if a propositional formula (example depicted) can be made true by an appropriate assignment of truth values to its variables.