**Description:** Membership law for union of classes. (Contributed by NM, 5-Aug-1993)

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

Assertion | elun1 | $${\u22a2}{A}\in {B}\to {A}\in \left({B}\cup {C}\right)$$ |

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

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

2 | 1 | sseli | $${\u22a2}{A}\in {B}\to {A}\in \left({B}\cup {C}\right)$$ |