(2.1) Let b>0 and X = [-b, b). Here we admit B"open" in 7 if and only if {0} ¢ B or (-b, b) C B. (a) Give all the closed sets in 7. (b) Let C = {}. What is Č? (c) Show that 0 is a limit point of any...

Extracted text: (2.1) Let b>0 and X = [-b, b). Here we admit B"open" in 7 if and only if {0} ¢ B or (-b, b) C B. (a) Give all the closed sets in 7. (b) Let C = {}. What is Č? (c) Show that 0 is a limit point of any subset of AC (-b, b).