With fff as in Q28, D={(x,y)∈R2:y≥f(x)}D=\{(x,y)\in\mathbb R^2:y\ge f(x)\}D={(x,y)∈R2:y≥f(x)} (epigraph of fff). Which is true?
R2∖D\mathbb R^2\setminus DR2∖D is convex
R+2∖D\mathbb R^2_+\setminus DR+2∖D is convex
DDD is not convex
None of the above
