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Metamath Proof Explorer

Theorem nnssz

Description: Positive integers are a subset of integers. (Contributed by NM, 9-Jan-2002)

Ref Expression
Assertion nnssz 
|- NN C_ ZZ

Proof

Step Hyp Ref Expression
1 nnz 
 |-  ( x e. NN -> x e. ZZ )
2 1 ssriv 
 |-  NN C_ ZZ