# Prove that $\text{int}(\text{dom}(f))$ is a convex set.

Let $f$ be a convex function. I have to prove that $\text{int}(\text{dom}(f))$ is a convex set. (Be careful with $-∞$ )

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What have you tried? –  Stefan Oct 31 '12 at 1:25
Why should he try anything? He is giving us commands. –  GEdgar Oct 31 '12 at 1:33
@Stefan Thansk for your quick reply. I can prove it for function like f:$\mathbb{R}^n$U{∞} case, but not sure what will happen for -∞ case for function defined like f:$\mathbb{R}^n$ U{∞}U{-∞} –  Abdul kadir Oct 31 '12 at 1:40
@GEdgar Why are you always so "reactive" with new users? –  Pedro Tamaroff Oct 31 '12 at 1:43
@GEdgar Well I removed the command part :) –  Abdul kadir Oct 31 '12 at 1:45