Metamath Proof Explorer

Theorem nnz

Description: A positive integer is an integer. (Contributed by NM, 9-May-2004)

Ref Expression
Assertion nnz 
|- ( N e. NN -> N e. ZZ )

Proof

Step Hyp Ref Expression
1 nnssz 
 |-  NN C_ ZZ
2 1 sseli 
 |-  ( N e. NN -> N e. ZZ )