# Metamath Proof Explorer

## Theorem expcn

Description: The power function on complex numbers, for fixed exponent N , is continuous. (Contributed by Mario Carneiro, 5-May-2014) (Revised by Mario Carneiro, 23-Aug-2014)

Ref Expression
Hypothesis expcn.j 𝐽 = ( TopOpen ‘ ℂfld )
Assertion expcn ( 𝑁 ∈ ℕ0 → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑁 ) ) ∈ ( 𝐽 Cn 𝐽 ) )

### Proof

Step Hyp Ref Expression
1 expcn.j 𝐽 = ( TopOpen ‘ ℂfld )
2 oveq2 ( 𝑛 = 0 → ( 𝑥𝑛 ) = ( 𝑥 ↑ 0 ) )
3 2 mpteq2dv ( 𝑛 = 0 → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) = ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ 0 ) ) )
4 3 eleq1d ( 𝑛 = 0 → ( ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) ∈ ( 𝐽 Cn 𝐽 ) ↔ ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ 0 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) )
5 oveq2 ( 𝑛 = 𝑘 → ( 𝑥𝑛 ) = ( 𝑥𝑘 ) )
6 5 mpteq2dv ( 𝑛 = 𝑘 → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) = ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) )
7 6 eleq1d ( 𝑛 = 𝑘 → ( ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) ∈ ( 𝐽 Cn 𝐽 ) ↔ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) )
8 oveq2 ( 𝑛 = ( 𝑘 + 1 ) → ( 𝑥𝑛 ) = ( 𝑥 ↑ ( 𝑘 + 1 ) ) )
9 8 mpteq2dv ( 𝑛 = ( 𝑘 + 1 ) → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) = ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) )
10 9 eleq1d ( 𝑛 = ( 𝑘 + 1 ) → ( ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) ∈ ( 𝐽 Cn 𝐽 ) ↔ ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) ∈ ( 𝐽 Cn 𝐽 ) ) )
11 oveq2 ( 𝑛 = 𝑁 → ( 𝑥𝑛 ) = ( 𝑥𝑁 ) )
12 11 mpteq2dv ( 𝑛 = 𝑁 → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) = ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑁 ) ) )
13 12 eleq1d ( 𝑛 = 𝑁 → ( ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑛 ) ) ∈ ( 𝐽 Cn 𝐽 ) ↔ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑁 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) )
14 exp0 ( 𝑥 ∈ ℂ → ( 𝑥 ↑ 0 ) = 1 )
15 14 mpteq2ia ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ 0 ) ) = ( 𝑥 ∈ ℂ ↦ 1 )
16 1 cnfldtopon 𝐽 ∈ ( TopOn ‘ ℂ )
17 16 a1i ( ⊤ → 𝐽 ∈ ( TopOn ‘ ℂ ) )
18 1cnd ( ⊤ → 1 ∈ ℂ )
19 17 17 18 cnmptc ( ⊤ → ( 𝑥 ∈ ℂ ↦ 1 ) ∈ ( 𝐽 Cn 𝐽 ) )
20 19 mptru ( 𝑥 ∈ ℂ ↦ 1 ) ∈ ( 𝐽 Cn 𝐽 )
21 15 20 eqeltri ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ 0 ) ) ∈ ( 𝐽 Cn 𝐽 )
22 oveq1 ( 𝑥 = 𝑛 → ( 𝑥 ↑ ( 𝑘 + 1 ) ) = ( 𝑛 ↑ ( 𝑘 + 1 ) ) )
23 22 cbvmptv ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) = ( 𝑛 ∈ ℂ ↦ ( 𝑛 ↑ ( 𝑘 + 1 ) ) )
24 id ( 𝑛 ∈ ℂ → 𝑛 ∈ ℂ )
25 simpl ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → 𝑘 ∈ ℕ0 )
26 expp1 ( ( 𝑛 ∈ ℂ ∧ 𝑘 ∈ ℕ0 ) → ( 𝑛 ↑ ( 𝑘 + 1 ) ) = ( ( 𝑛𝑘 ) · 𝑛 ) )
27 24 25 26 syl2anr ( ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) ∧ 𝑛 ∈ ℂ ) → ( 𝑛 ↑ ( 𝑘 + 1 ) ) = ( ( 𝑛𝑘 ) · 𝑛 ) )
28 27 mpteq2dva ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑛 ∈ ℂ ↦ ( 𝑛 ↑ ( 𝑘 + 1 ) ) ) = ( 𝑛 ∈ ℂ ↦ ( ( 𝑛𝑘 ) · 𝑛 ) ) )
29 23 28 syl5eq ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) = ( 𝑛 ∈ ℂ ↦ ( ( 𝑛𝑘 ) · 𝑛 ) ) )
30 16 a1i ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → 𝐽 ∈ ( TopOn ‘ ℂ ) )
31 oveq1 ( 𝑥 = 𝑛 → ( 𝑥𝑘 ) = ( 𝑛𝑘 ) )
32 31 cbvmptv ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) = ( 𝑛 ∈ ℂ ↦ ( 𝑛𝑘 ) )
33 simpr ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) )
34 32 33 eqeltrrid ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑛 ∈ ℂ ↦ ( 𝑛𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) )
35 30 cnmptid ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑛 ∈ ℂ ↦ 𝑛 ) ∈ ( 𝐽 Cn 𝐽 ) )
36 1 mulcn · ∈ ( ( 𝐽 ×t 𝐽 ) Cn 𝐽 )
37 36 a1i ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → · ∈ ( ( 𝐽 ×t 𝐽 ) Cn 𝐽 ) )
38 30 34 35 37 cnmpt12f ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑛 ∈ ℂ ↦ ( ( 𝑛𝑘 ) · 𝑛 ) ) ∈ ( 𝐽 Cn 𝐽 ) )
39 29 38 eqeltrd ( ( 𝑘 ∈ ℕ0 ∧ ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) ) → ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) ∈ ( 𝐽 Cn 𝐽 ) )
40 39 ex ( 𝑘 ∈ ℕ0 → ( ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑘 ) ) ∈ ( 𝐽 Cn 𝐽 ) → ( 𝑥 ∈ ℂ ↦ ( 𝑥 ↑ ( 𝑘 + 1 ) ) ) ∈ ( 𝐽 Cn 𝐽 ) ) )
41 4 7 10 13 21 40 nn0ind ( 𝑁 ∈ ℕ0 → ( 𝑥 ∈ ℂ ↦ ( 𝑥𝑁 ) ) ∈ ( 𝐽 Cn 𝐽 ) )