**Description:** Closure of square. (Contributed by Mario Carneiro, 28-May-2016)

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

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

Assertion | sqcld | $${\u22a2}{\phi}\to {{A}}^{2}\in \u2102$$ |

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

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

2 | sqcl | $${\u22a2}{A}\in \u2102\to {{A}}^{2}\in \u2102$$ | |

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