1. The problem statement, all variables and given/known data Show [0,1] is not open in ℝ 2. Relevant equations [0,1] is open if and only if ℝ\[0,1] is closed. 3. The attempt at a solution ℝ\[0,1] = (-∞,0) U (1,∞), this set is open. Despite the if and only if statement this is enough to say that [0,1] is not open in ℝ. Is this correct?