When the full power of SAT is not required to prove a language is in NPC, 3-CNF provides a more constrained alternative.

k-CNF (Conjunctive Normal Form) is a formula having a conjunction of
**clauses**, where each clause is a disjunction of exactly k literals
(variable or its negation).

Example 3-CNF:

**Theorem 36.10**

3-CNF-SAT NPC