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Theorem exss 5076
 Description: Restricted existence in a class (even if proper) implies restricted existence in a subset. (Contributed by NM, 23-Aug-2003.)
Assertion
Ref Expression
exss (∃𝑥𝐴 𝜑 → ∃𝑦(𝑦𝐴 ∧ ∃𝑥𝑦 𝜑))
Distinct variable groups:   𝑥,𝑦,𝐴   𝜑,𝑦
Allowed substitution hint:   𝜑(𝑥)

Proof of Theorem exss
Dummy variable 𝑧 is distinct from all other variables.
StepHypRef Expression
1 df-rab 3055 . . . 4 {𝑥𝐴𝜑} = {𝑥 ∣ (𝑥𝐴𝜑)}
21neeq1i 2992 . . 3 ({𝑥𝐴𝜑} ≠ ∅ ↔ {𝑥 ∣ (𝑥𝐴𝜑)} ≠ ∅)
3 rabn0 4097 . . 3 ({𝑥𝐴𝜑} ≠ ∅ ↔ ∃𝑥𝐴 𝜑)
4 n0 4070 . . 3 ({𝑥 ∣ (𝑥𝐴𝜑)} ≠ ∅ ↔ ∃𝑧 𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)})
52, 3, 43bitr3i 290 . 2 (∃𝑥𝐴 𝜑 ↔ ∃𝑧 𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)})
6 vex 3339 . . . . . 6 𝑧 ∈ V
76snss 4456 . . . . 5 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} ↔ {𝑧} ⊆ {𝑥 ∣ (𝑥𝐴𝜑)})
8 ssab2 3823 . . . . . 6 {𝑥 ∣ (𝑥𝐴𝜑)} ⊆ 𝐴
9 sstr2 3747 . . . . . 6 ({𝑧} ⊆ {𝑥 ∣ (𝑥𝐴𝜑)} → ({𝑥 ∣ (𝑥𝐴𝜑)} ⊆ 𝐴 → {𝑧} ⊆ 𝐴))
108, 9mpi 20 . . . . 5 ({𝑧} ⊆ {𝑥 ∣ (𝑥𝐴𝜑)} → {𝑧} ⊆ 𝐴)
117, 10sylbi 207 . . . 4 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → {𝑧} ⊆ 𝐴)
12 simpr 479 . . . . . . . 8 (([𝑧 / 𝑥]𝑥𝐴 ∧ [𝑧 / 𝑥]𝜑) → [𝑧 / 𝑥]𝜑)
13 equsb1 2501 . . . . . . . . 9 [𝑧 / 𝑥]𝑥 = 𝑧
14 velsn 4333 . . . . . . . . . 10 (𝑥 ∈ {𝑧} ↔ 𝑥 = 𝑧)
1514sbbii 2049 . . . . . . . . 9 ([𝑧 / 𝑥]𝑥 ∈ {𝑧} ↔ [𝑧 / 𝑥]𝑥 = 𝑧)
1613, 15mpbir 221 . . . . . . . 8 [𝑧 / 𝑥]𝑥 ∈ {𝑧}
1712, 16jctil 561 . . . . . . 7 (([𝑧 / 𝑥]𝑥𝐴 ∧ [𝑧 / 𝑥]𝜑) → ([𝑧 / 𝑥]𝑥 ∈ {𝑧} ∧ [𝑧 / 𝑥]𝜑))
18 df-clab 2743 . . . . . . . 8 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} ↔ [𝑧 / 𝑥](𝑥𝐴𝜑))
19 sban 2532 . . . . . . . 8 ([𝑧 / 𝑥](𝑥𝐴𝜑) ↔ ([𝑧 / 𝑥]𝑥𝐴 ∧ [𝑧 / 𝑥]𝜑))
2018, 19bitri 264 . . . . . . 7 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} ↔ ([𝑧 / 𝑥]𝑥𝐴 ∧ [𝑧 / 𝑥]𝜑))
21 df-rab 3055 . . . . . . . . 9 {𝑥 ∈ {𝑧} ∣ 𝜑} = {𝑥 ∣ (𝑥 ∈ {𝑧} ∧ 𝜑)}
2221eleq2i 2827 . . . . . . . 8 (𝑧 ∈ {𝑥 ∈ {𝑧} ∣ 𝜑} ↔ 𝑧 ∈ {𝑥 ∣ (𝑥 ∈ {𝑧} ∧ 𝜑)})
23 df-clab 2743 . . . . . . . . 9 (𝑧 ∈ {𝑥 ∣ (𝑥 ∈ {𝑧} ∧ 𝜑)} ↔ [𝑧 / 𝑥](𝑥 ∈ {𝑧} ∧ 𝜑))
24 sban 2532 . . . . . . . . 9 ([𝑧 / 𝑥](𝑥 ∈ {𝑧} ∧ 𝜑) ↔ ([𝑧 / 𝑥]𝑥 ∈ {𝑧} ∧ [𝑧 / 𝑥]𝜑))
2523, 24bitri 264 . . . . . . . 8 (𝑧 ∈ {𝑥 ∣ (𝑥 ∈ {𝑧} ∧ 𝜑)} ↔ ([𝑧 / 𝑥]𝑥 ∈ {𝑧} ∧ [𝑧 / 𝑥]𝜑))
2622, 25bitri 264 . . . . . . 7 (𝑧 ∈ {𝑥 ∈ {𝑧} ∣ 𝜑} ↔ ([𝑧 / 𝑥]𝑥 ∈ {𝑧} ∧ [𝑧 / 𝑥]𝜑))
2717, 20, 263imtr4i 281 . . . . . 6 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → 𝑧 ∈ {𝑥 ∈ {𝑧} ∣ 𝜑})
28 ne0i 4060 . . . . . 6 (𝑧 ∈ {𝑥 ∈ {𝑧} ∣ 𝜑} → {𝑥 ∈ {𝑧} ∣ 𝜑} ≠ ∅)
2927, 28syl 17 . . . . 5 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → {𝑥 ∈ {𝑧} ∣ 𝜑} ≠ ∅)
30 rabn0 4097 . . . . 5 ({𝑥 ∈ {𝑧} ∣ 𝜑} ≠ ∅ ↔ ∃𝑥 ∈ {𝑧}𝜑)
3129, 30sylib 208 . . . 4 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → ∃𝑥 ∈ {𝑧}𝜑)
32 snex 5053 . . . . 5 {𝑧} ∈ V
33 sseq1 3763 . . . . . 6 (𝑦 = {𝑧} → (𝑦𝐴 ↔ {𝑧} ⊆ 𝐴))
34 rexeq 3274 . . . . . 6 (𝑦 = {𝑧} → (∃𝑥𝑦 𝜑 ↔ ∃𝑥 ∈ {𝑧}𝜑))
3533, 34anbi12d 749 . . . . 5 (𝑦 = {𝑧} → ((𝑦𝐴 ∧ ∃𝑥𝑦 𝜑) ↔ ({𝑧} ⊆ 𝐴 ∧ ∃𝑥 ∈ {𝑧}𝜑)))
3632, 35spcev 3436 . . . 4 (({𝑧} ⊆ 𝐴 ∧ ∃𝑥 ∈ {𝑧}𝜑) → ∃𝑦(𝑦𝐴 ∧ ∃𝑥𝑦 𝜑))
3711, 31, 36syl2anc 696 . . 3 (𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → ∃𝑦(𝑦𝐴 ∧ ∃𝑥𝑦 𝜑))
3837exlimiv 2003 . 2 (∃𝑧 𝑧 ∈ {𝑥 ∣ (𝑥𝐴𝜑)} → ∃𝑦(𝑦𝐴 ∧ ∃𝑥𝑦 𝜑))
395, 38sylbi 207 1 (∃𝑥𝐴 𝜑 → ∃𝑦(𝑦𝐴 ∧ ∃𝑥𝑦 𝜑))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 383   = wceq 1628  ∃wex 1849  [wsb 2042   ∈ wcel 2135  {cab 2742   ≠ wne 2928  ∃wrex 3047  {crab 3050   ⊆ wss 3711  ∅c0 4054  {csn 4317 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1867  ax-4 1882  ax-5 1984  ax-6 2050  ax-7 2086  ax-9 2144  ax-10 2164  ax-11 2179  ax-12 2192  ax-13 2387  ax-ext 2736  ax-sep 4929  ax-nul 4937  ax-pr 5051 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-3an 1074  df-tru 1631  df-ex 1850  df-nf 1855  df-sb 2043  df-clab 2743  df-cleq 2749  df-clel 2752  df-nfc 2887  df-ne 2929  df-ral 3051  df-rex 3052  df-rab 3055  df-v 3338  df-dif 3714  df-un 3716  df-in 3718  df-ss 3725  df-nul 4055  df-sn 4318  df-pr 4320 This theorem is referenced by: (None)
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