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| Mirrors > Home > MPE Home > Th. List > ssun1 | Structured version Visualization version GIF version | ||
| Description: Subclass relationship for union of classes. Theorem 25 of [Suppes] p. 27. (Contributed by NM, 5-Aug-1993.) |
| Ref | Expression |
|---|---|
| ssun1 | ⊢ 𝐴 ⊆ (𝐴 ∪ 𝐵) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | orc 867 | . . 3 ⊢ (𝑥 ∈ 𝐴 → (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)) | |
| 2 | elun 4135 | . . 3 ⊢ (𝑥 ∈ (𝐴 ∪ 𝐵) ↔ (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)) | |
| 3 | 1, 2 | sylibr 234 | . 2 ⊢ (𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐴 ∪ 𝐵)) |
| 4 | 3 | ssriv 3969 | 1 ⊢ 𝐴 ⊆ (𝐴 ∪ 𝐵) |
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