Metamath Proof Explorer

Theorem nn0zi

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

Ref Expression
Hypothesis nn0zi.1 
|- N e. NN0
Assertion nn0zi 
|- N e. ZZ

Proof

Step Hyp Ref Expression
1 nn0zi.1 
 |-  N e. NN0
2 nn0ssz 
 |-  NN0 C_ ZZ
3 2 1 sselii 
 |-  N e. ZZ