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Metamath Proof Explorer

Theorem nnon

Description: A natural number is an ordinal number. (Contributed by NM, 27-Jun-1994)

Ref Expression
Assertion nnon 
|- ( A e. _om -> A e. On )

Proof

Step Hyp Ref Expression
1 omsson 
 |-  _om C_ On
2 1 sseli 
 |-  ( A e. _om -> A e. On )