c3 domains

I'm confused when you have to state that x ∈ R.

e.g. is it okay to state 0 < x < 3 and x ∈ R, or does this not make 'grammatical' sense. If so, when should i use x ∈ R?

I'm confused when you have to state that x ∈ R.

e.g. is it okay to state 0 < x < 3 and x ∈ R, or does this not make 'grammatical' sense. If so, when should i use x ∈ R? what about for x > 0 and x ∈ R, where the domain is 'less restricted' so to speak

You should specify x in R each time

There is no need for the and