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

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

Assertion | elun2 | $${\u22a2}{A}\in {B}\to {A}\in \left({C}\cup {B}\right)$$ |

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

1 | ssun2 | $${\u22a2}{B}\subseteq {C}\cup {B}$$ | |

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