Metamath Proof Explorer


Theorem nnzi

Description: A positive integer is an integer. (Contributed by Mario Carneiro, 18-Feb-2014)

Ref Expression
Hypothesis nnzi.1
|- N e. NN
Assertion nnzi
|- N e. ZZ

Proof

Step Hyp Ref Expression
1 nnzi.1
 |-  N e. NN
2 nnssz
 |-  NN C_ ZZ
3 2 1 sselii
 |-  N e. ZZ