This is an inofficial mirror of http://metamath.tirix.org for personal testing of a visualizer extension only.

Metamath Proof Explorer

Theorem 1z

Description: One is an integer. (Contributed by NM, 10-May-2004)

Ref Expression
Assertion 1z 
|- 1 e. ZZ

Proof

Step Hyp Ref Expression
1 1nn 
 |-  1 e. NN
2 1 nnzi 
 |-  1 e. ZZ