I am looking for a proof that (N,+) is rigid. A model is rigid if its
only automorphism is the identity function.  Here N is the set of
natural numbers.

I can answer this question, you have to demontrate first that the
onlhy bijection from N to N that increasing is the identity. Then
demonstrate that you automorphism is increasing...

Tell me how to use this site please, it's my first use of it