**Description:** Closure of half of a number (frequently used special case).
(Contributed by Mario Carneiro, 27-May-2016)

Ref | Expression | ||
---|---|---|---|

Hypothesis | 2timesd.1 | $${\u22a2}{\phi}\to {A}\in \u2102$$ | |

Assertion | halfcld | $${\u22a2}{\phi}\to \frac{{A}}{2}\in \u2102$$ |

Step | Hyp | Ref | Expression |
---|---|---|---|

1 | 2timesd.1 | $${\u22a2}{\phi}\to {A}\in \u2102$$ | |

2 | halfcl | $${\u22a2}{A}\in \u2102\to \frac{{A}}{2}\in \u2102$$ | |

3 | 1 2 | syl | $${\u22a2}{\phi}\to \frac{{A}}{2}\in \u2102$$ |