Recall SAT is in NP because if \phi \in \text{SAT}, then there is a short (poly-n space), efficiently (poly-time) checkable proof (by just reading out the satisfying assignment).
Recall SAT is in NP because if \phi \in \text{SAT}, then there is a short (poly-n space), efficiently (poly-time) checkable proof (by just reading out the satisfying assignment).