Metamath Proof Explorer

Theorem nn0z

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

Ref Expression
Assertion nn0z 
|- ( N e. NN0 -> N e. ZZ )

Proof

Step Hyp Ref Expression
1 nn0ssz 
 |-  NN0 C_ ZZ
2 1 sseli 
 |-  ( N e. NN0 -> N e. ZZ )