Question: Working with 'argument'

Especially in old books (but not only there) the authors prefer the notion
of 'argument' ( = polar coordinates and using the angle).

Sometimes it comes to something like 

                | arg(-z) | < Pi and | arg(1 - z) | < Pi

which I prefer to have in terms of interval notation 'z in ... ' or its
complement  'not (z in .. )'.

I do not even know how to get | arg(z) | < Pi  <==> z is not a negative Real. 

How can I do it in Maple?
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