| Step | Hyp | Ref
 | Expression | 
| 1 |   | simpr 110 | 
. . . . . . . 8
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → 𝑇 ⊆ ℂ) | 
| 2 |   | cnex 8003 | 
. . . . . . . 8
⊢ ℂ
∈ V | 
| 3 |   | ssexg 4172 | 
. . . . . . . 8
⊢ ((𝑇 ⊆ ℂ ∧ ℂ
∈ V) → 𝑇 ∈
V) | 
| 4 | 1, 2, 3 | sylancl 413 | 
. . . . . . 7
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → 𝑇 ∈ V) | 
| 5 |   | c0ex 8020 | 
. . . . . . . 8
⊢ 0 ∈
V | 
| 6 | 5 | snex 4218 | 
. . . . . . 7
⊢ {0}
∈ V | 
| 7 |   | unexg 4478 | 
. . . . . . 7
⊢ ((𝑇 ∈ V ∧ {0} ∈ V)
→ (𝑇 ∪ {0}) ∈
V) | 
| 8 | 4, 6, 7 | sylancl 413 | 
. . . . . 6
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (𝑇 ∪ {0}) ∈ V) | 
| 9 |   | unss1 3332 | 
. . . . . . 7
⊢ (𝑆 ⊆ 𝑇 → (𝑆 ∪ {0}) ⊆ (𝑇 ∪ {0})) | 
| 10 | 9 | adantr 276 | 
. . . . . 6
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (𝑆 ∪ {0}) ⊆ (𝑇 ∪ {0})) | 
| 11 |   | mapss 6750 | 
. . . . . 6
⊢ (((𝑇 ∪ {0}) ∈ V ∧
(𝑆 ∪ {0}) ⊆
(𝑇 ∪ {0})) →
((𝑆 ∪ {0})
↑𝑚 ℕ0) ⊆ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)) | 
| 12 | 8, 10, 11 | syl2anc 411 | 
. . . . 5
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → ((𝑆 ∪ {0}) ↑𝑚
ℕ0) ⊆ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)) | 
| 13 |   | ssrexv 3248 | 
. . . . 5
⊢ (((𝑆 ∪ {0})
↑𝑚 ℕ0) ⊆ ((𝑇 ∪ {0}) ↑𝑚
ℕ0) → (∃𝑎 ∈ ((𝑆 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))) → ∃𝑎 ∈ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))))) | 
| 14 | 12, 13 | syl 14 | 
. . . 4
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (∃𝑎 ∈ ((𝑆 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))) → ∃𝑎 ∈ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))))) | 
| 15 | 14 | reximdv 2598 | 
. . 3
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (∃𝑛 ∈ ℕ0
∃𝑎 ∈ ((𝑆 ∪ {0})
↑𝑚 ℕ0)𝑓 = (𝑧 ∈ ℂ ↦ Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))) → ∃𝑛 ∈ ℕ0 ∃𝑎 ∈ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘))))) | 
| 16 | 15 | ss2abdv 3256 | 
. 2
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → {𝑓 ∣ ∃𝑛 ∈ ℕ0 ∃𝑎 ∈ ((𝑆 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))} ⊆ {𝑓 ∣ ∃𝑛 ∈ ℕ0 ∃𝑎 ∈ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))}) | 
| 17 |   | sstr 3191 | 
. . 3
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → 𝑆 ⊆ ℂ) | 
| 18 |   | plyval 14968 | 
. . 3
⊢ (𝑆 ⊆ ℂ →
(Poly‘𝑆) = {𝑓 ∣ ∃𝑛 ∈ ℕ0
∃𝑎 ∈ ((𝑆 ∪ {0})
↑𝑚 ℕ0)𝑓 = (𝑧 ∈ ℂ ↦ Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))}) | 
| 19 | 17, 18 | syl 14 | 
. 2
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (Poly‘𝑆) = {𝑓 ∣ ∃𝑛 ∈ ℕ0 ∃𝑎 ∈ ((𝑆 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))}) | 
| 20 |   | plyval 14968 | 
. . 3
⊢ (𝑇 ⊆ ℂ →
(Poly‘𝑇) = {𝑓 ∣ ∃𝑛 ∈ ℕ0
∃𝑎 ∈ ((𝑇 ∪ {0})
↑𝑚 ℕ0)𝑓 = (𝑧 ∈ ℂ ↦ Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))}) | 
| 21 | 20 | adantl 277 | 
. 2
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (Poly‘𝑇) = {𝑓 ∣ ∃𝑛 ∈ ℕ0 ∃𝑎 ∈ ((𝑇 ∪ {0}) ↑𝑚
ℕ0)𝑓 =
(𝑧 ∈ ℂ ↦
Σ𝑘 ∈ (0...𝑛)((𝑎‘𝑘) · (𝑧↑𝑘)))}) | 
| 22 | 16, 19, 21 | 3sstr4d 3228 | 
1
⊢ ((𝑆 ⊆ 𝑇 ∧ 𝑇 ⊆ ℂ) → (Poly‘𝑆) ⊆ (Poly‘𝑇)) |