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 | contextually convertible to bool | !(a == b) | |

a == np | contextually convertible to bool | a == P() | |

np == a | |||

a != np | contextually convertible to bool | !(a == np) | |

np != a |