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Mirrors > Home > MPE Home > Th. List > nnullss | Structured version Visualization version GIF version |
Description: A nonempty class (even if proper) has a nonempty subset. (Contributed by NM, 23-Aug-2003.) |
Ref | Expression |
---|---|
nnullss | ⊢ (𝐴 ≠ ∅ → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | n0 4260 | . 2 ⊢ (𝐴 ≠ ∅ ↔ ∃𝑦 𝑦 ∈ 𝐴) | |
2 | vex 3444 | . . . . 5 ⊢ 𝑦 ∈ V | |
3 | 2 | snss 4679 | . . . 4 ⊢ (𝑦 ∈ 𝐴 ↔ {𝑦} ⊆ 𝐴) |
4 | 2 | snnz 4672 | . . . . 5 ⊢ {𝑦} ≠ ∅ |
5 | snex 5297 | . . . . . 6 ⊢ {𝑦} ∈ V | |
6 | sseq1 3940 | . . . . . . 7 ⊢ (𝑥 = {𝑦} → (𝑥 ⊆ 𝐴 ↔ {𝑦} ⊆ 𝐴)) | |
7 | neeq1 3049 | . . . . . . 7 ⊢ (𝑥 = {𝑦} → (𝑥 ≠ ∅ ↔ {𝑦} ≠ ∅)) | |
8 | 6, 7 | anbi12d 633 | . . . . . 6 ⊢ (𝑥 = {𝑦} → ((𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅) ↔ ({𝑦} ⊆ 𝐴 ∧ {𝑦} ≠ ∅))) |
9 | 5, 8 | spcev 3555 | . . . . 5 ⊢ (({𝑦} ⊆ 𝐴 ∧ {𝑦} ≠ ∅) → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
10 | 4, 9 | mpan2 690 | . . . 4 ⊢ ({𝑦} ⊆ 𝐴 → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
11 | 3, 10 | sylbi 220 | . . 3 ⊢ (𝑦 ∈ 𝐴 → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
12 | 11 | exlimiv 1931 | . 2 ⊢ (∃𝑦 𝑦 ∈ 𝐴 → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
13 | 1, 12 | sylbi 220 | 1 ⊢ (𝐴 ≠ ∅ → ∃𝑥(𝑥 ⊆ 𝐴 ∧ 𝑥 ≠ ∅)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 399 = wceq 1538 ∃wex 1781 ∈ wcel 2111 ≠ wne 2987 ⊆ wss 3881 ∅c0 4243 {csn 4525 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1797 ax-4 1811 ax-5 1911 ax-6 1970 ax-7 2015 ax-8 2113 ax-9 2121 ax-12 2175 ax-ext 2770 ax-sep 5167 ax-nul 5174 ax-pr 5295 |
This theorem depends on definitions: df-bi 210 df-an 400 df-or 845 df-3an 1086 df-tru 1541 df-ex 1782 df-nf 1786 df-sb 2070 df-clab 2777 df-cleq 2791 df-clel 2870 df-ne 2988 df-v 3443 df-dif 3884 df-un 3886 df-in 3888 df-ss 3898 df-nul 4244 df-sn 4526 df-pr 4528 |
This theorem is referenced by: (None) |
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