| Expression | Return type | Operational semantics | 
| P u(np); | Postconditions: u == nullptr | |
| P u = np; | ||
| P(np) | Postconditions: P(np) == nullptr | |
| t = np | P& | Postconditions: t == nullptr | 
| a != b | decltype(a != b) models boolean-testable | !(a == b) | 
| a == np | a == P() | |
| np == a | ||
| a != np | !(a == np) | |
| np != a |