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Metamath Proof Explorer

Theorem nnssnn0

Description: Positive naturals are a subset of nonnegative integers. (Contributed by Raph Levien, 10-Dec-2002)

Ref Expression
Assertion nnssnn0 
|- NN C_ NN0

Proof

Step Hyp Ref Expression
1 ssun1 
 |-  NN C_ ( NN u. { 0 } )
2 df-n0 
 |-  NN0 = ( NN u. { 0 } )
3 1 2 sseqtrri 
 |-  NN C_ NN0