Parentheses mean that you can't get the value here, and the landmarks in parentheses can get the value here.

X ∈ (100,200), which means: 100 < x < 200.

X ∈100,200), that is, 100 ≤ X < 200.

X ∈ (100,200, meaning: 100 < x ≤ 200.

X ∈100,200 means: 100≤x≤200.