Show that r≤Rr \leq R and ‖a−b‖≤R−r\big\| a-b \big\| \leq R-r [on hold]

Since \overline{S}_r(a)\subset \overline{S}_R(b)\subset X\overline{S}_r(a)\subset \overline{S}_R(b)\subset X. Show that r \leq Rr \leq R and \big\| a-b \big\| \leq R-r\big\| a-b \big\| \leq R-r

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