Each clause has several literals . Determining the satisfiability of a formula in conjunctive normal form where each clause is limited to at most three literals is NP-complete ; this problem is called `` 3SAT '' , `` 3CNFSAT '' , or `` 3-satisfiability '' . Determining the satisfiability of a formula in which each clause is limited to at most two literals is NL-complete ; this problem is called `` 2SAT '' .