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Mirrors > Home > MPE Home > Th. List > pssdifn0 | Structured version Visualization version GIF version |
Description: A proper subclass has a nonempty difference. (Contributed by NM, 3-May-1994.) |
Ref | Expression |
---|---|
pssdifn0 | ⊢ ((𝐴 ⊆ 𝐵 ∧ 𝐴 ≠ 𝐵) → (𝐵 ∖ 𝐴) ≠ ∅) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ssdif0 4325 | . . . 4 ⊢ (𝐵 ⊆ 𝐴 ↔ (𝐵 ∖ 𝐴) = ∅) | |
2 | eqss 3984 | . . . . 5 ⊢ (𝐴 = 𝐵 ↔ (𝐴 ⊆ 𝐵 ∧ 𝐵 ⊆ 𝐴)) | |
3 | 2 | simplbi2 503 | . . . 4 ⊢ (𝐴 ⊆ 𝐵 → (𝐵 ⊆ 𝐴 → 𝐴 = 𝐵)) |
4 | 1, 3 | syl5bir 245 | . . 3 ⊢ (𝐴 ⊆ 𝐵 → ((𝐵 ∖ 𝐴) = ∅ → 𝐴 = 𝐵)) |
5 | 4 | necon3d 3039 | . 2 ⊢ (𝐴 ⊆ 𝐵 → (𝐴 ≠ 𝐵 → (𝐵 ∖ 𝐴) ≠ ∅)) |
6 | 5 | imp 409 | 1 ⊢ ((𝐴 ⊆ 𝐵 ∧ 𝐴 ≠ 𝐵) → (𝐵 ∖ 𝐴) ≠ ∅) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 398 = wceq 1537 ≠ wne 3018 ∖ cdif 3935 ⊆ wss 3938 ∅c0 4293 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1911 ax-6 1970 ax-7 2015 ax-8 2116 ax-9 2124 ax-10 2145 ax-11 2161 ax-12 2177 ax-ext 2795 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-tru 1540 df-ex 1781 df-nf 1785 df-sb 2070 df-clab 2802 df-cleq 2816 df-clel 2895 df-nfc 2965 df-ne 3019 df-v 3498 df-dif 3941 df-in 3945 df-ss 3954 df-nul 4294 |
This theorem is referenced by: pssdif 4328 tz7.7 6219 domdifsn 8602 inf3lem3 9095 isf32lem6 9782 fclscf 22635 flimfnfcls 22638 lebnumlem1 23567 lebnumlem2 23568 lebnumlem3 23569 ig1peu 24767 ig1pdvds 24772 qsidomlem2 30968 divrngidl 35308 |
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