the upper keyboard part can have an independent structure from the other voices: that happens in the broken chord semiquavers or triplets that give bach's predetermined realisation of a figured bass in the slow movements of bwv 1017; and also in bwv 1016/1 where it is divided into three voices. in the accompanying keyboard ritornello of the first movement of the f minor sonata bwv 1018, the two parts in the upper keyboard and the bass line share the same material which is echoed imitatively between them; in the third movement of the same sonata, the filigree demisemiquaver scale figures in the right hand are responded to by demisemiquaver arpeggios in the left hand.