In detail, given a median-selection algorithm, one can use it as a pivot strategy in Quickselect, obtaining a selection algorithm. If the median-selection algorithm is optimal, meaning O("n"), then the resulting general selection algorithm is also optimal, again meaning linear. This is because Quickselect is a divide and conquer algorithm, and using the median at each pivot means that at each step the search set decreases by half in size, so the overall complexity is a geometric series times the complexity of each step, and thus simply a constant times the complexity of a single step, in fact formula_2 times (summing the series).