Theorem dfnn2 9239

Description: Definition of the set of positive integers. Another name for df-inn 9238. (Contributed by Jeff Hankins, 12-Sep-2013.) (Revised by Mario Carneiro, 3-May-2014.)

Assertion

Ref	Expression
dfnn2	⊢ ℕ = ∩ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦 ∈ 𝑥 (𝑦 + 1) ∈ 𝑥)}

Distinct variable group:   𝑥,𝑦

Proof of Theorem dfnn2

Step	Hyp	Ref	Expression
1		df-inn 9238	1 ⊢ ℕ = ∩ {𝑥 ∣ (1 ∈ 𝑥 ∧ ∀𝑦 ∈ 𝑥 (𝑦 + 1) ∈ 𝑥)}

Syntax hints:   ∧ wa 104   = wceq 1398   ∈ wcel 2203  {cab 2218  ∀wral 2520  ∩ cint 3949  (class class class)co 6050  1c1 8128   + caddc 8130  ℕcn 9237

This theorem depends on definitions:  df-inn 9238

This theorem is referenced by:  peano5nni  9240  1nn  9248  peano2nn  9249  arch  9493  caucvgre  11666