[0GD]Note that \(A⊇ {{A}^\circ }\) and \(B⊆ \overline B\), generally. Show that \(A\) is open if and only if \(A={{A}^\circ }\); and that \(B\) is closed if and only if \(B=\overline B\), using definitions [0G6]↺↻ and [0G7]↺↻.
