A port-multiplexed system are disclosed. The exhaust system includes an exhaust channel with a main catalytic converter disposed therein, a bypass channel with a bypass catalytic converter disposed therein, and a valve mechanism disposed in the exhaust channel between the connection points of the exhaust channel to switch a pathway for exhaust gas from the exhaust channel to the bypass channel. The position of the lower arms is optimized to apply a constant pressure to the muscles above the hip joint providing relief from so-called hip pain associated with many pregnancies. One or more single mobile drive units may be used to transport inventory holders to and from a region, and one or more other mobile drive units may be used to reposition or slide each of the inventory holders back and forth within the region to efficiently place inventory holders before an operator on an as-needed basis. The first solution and the second are mixed to form a third solution.