14970 | Normal system K has five axioms and rules |

14971 | D is valid on every serial frame, but not where there are dead ends |

14972 | S4 has 14 modalities, and always reduces to a maximum of three modal operators |

14973 | In S5 all the long complex modalities reduce to just three, and their negations |

14976 | Reject the Barcan if quantifiers are confined to worlds, and different things exist in other worlds |

14974 | A relation is 'Euclidean' if aRb and aRc imply bRc |

14975 | A de dicto necessity is true in all worlds, but not necessarily of the same thing in each world |