**Description:** Subclass relationship for union of classes. (Contributed by NM, 30-Aug-1993)

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

Assertion | ssun2 | $${\u22a2}{A}\subseteq {B}\cup {A}$$ |

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

1 | ssun1 | $${\u22a2}{A}\subseteq {A}\cup {B}$$ | |

2 | uncom | $${\u22a2}{A}\cup {B}={B}\cup {A}$$ | |

3 | 1 2 | sseqtri | $${\u22a2}{A}\subseteq {B}\cup {A}$$ |