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| Mirrors > Home > MPE Home > Th. List > dfss3 | Structured version Visualization version GIF version | ||
| Description: Alternate definition of subclass relationship. (Contributed by NM, 14-Oct-1999.) |
| Ref | Expression |
|---|---|
| dfss3 | ⊢ (𝐴 ⊆ 𝐵 ↔ ∀𝑥 ∈ 𝐴 𝑥 ∈ 𝐵) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | df-ss 3968 | . 2 ⊢ (𝐴 ⊆ 𝐵 ↔ ∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵)) | |
| 2 | df-ral 3062 | . 2 ⊢ (∀𝑥 ∈ 𝐴 𝑥 ∈ 𝐵 ↔ ∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵)) | |
| 3 | 1, 2 | bitr4i 278 | 1 ⊢ (𝐴 ⊆ 𝐵 ↔ ∀𝑥 ∈ 𝐴 𝑥 ∈ 𝐵) |
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