For example,
set $A = \left \{ 1, 5, 10, 30 \right \} \in \mathbb{R}^N$
r = $10$
How do I write down a set which takes $A - r$ as lower bound, and $A + r$ as upper bound, containing ranges?
like:
set $C = (A - r)?(A+r) = \left \{ [-9,11], [-5,15], [0,20], [20, 40] \right \} \in \mathbb{R}^?$
Are there any notation that could describe such $?$ operation?
If I want to know if a number is in $C$
Is it okay to use, for example $(A-r)<m<(A+r)$?