Step | Hyp | Ref
| Expression |
1 | | 1ex 10877 |
. . . 4
⊢ 1 ∈
V |
2 | | fr0g 8213 |
. . . 4
⊢ (1 ∈
V → ((rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω)‘∅) = 1) |
3 | 1, 2 | ax-mp 5 |
. . 3
⊢
((rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω)‘∅) = 1 |
4 | | frfnom 8212 |
. . . 4
⊢
(rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω) Fn ω |
5 | | peano1 7707 |
. . . 4
⊢ ∅
∈ ω |
6 | | fnfvelrn 6937 |
. . . 4
⊢
(((rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω) Fn ω ∧ ∅ ∈ ω) → ((rec((𝑥 ∈ V ↦ (𝑥 + 1)), 1) ↾
ω)‘∅) ∈ ran (rec((𝑥 ∈ V ↦ (𝑥 + 1)), 1) ↾ ω)) |
7 | 4, 5, 6 | mp2an 692 |
. . 3
⊢
((rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω)‘∅) ∈ ran (rec((𝑥 ∈ V ↦ (𝑥 + 1)), 1) ↾ ω) |
8 | 3, 7 | eqeltrri 2837 |
. 2
⊢ 1 ∈
ran (rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω) |
9 | | df-nn 11879 |
. . 3
⊢ ℕ =
(rec((𝑥 ∈ V ↦
(𝑥 + 1)), 1) “
ω) |
10 | | df-ima 5592 |
. . 3
⊢
(rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
“ ω) = ran (rec((𝑥 ∈ V ↦ (𝑥 + 1)), 1) ↾ ω) |
11 | 9, 10 | eqtri 2767 |
. 2
⊢ ℕ =
ran (rec((𝑥 ∈ V
↦ (𝑥 + 1)), 1)
↾ ω) |
12 | 8, 11 | eleqtrri 2839 |
1
⊢ 1 ∈
ℕ |