Driving pulley 1 is connected to idle pulleys 2 and 3 by open belt 4 and crossed belt 5. Either one of the belts is shifted to driven working pulley 6 by means of link-gear belt shifter 7. The transmission ratios of the open and crossed belt drives are the same but of opposite sign (reversing the rotation of pulley 6).
$989$LG,4L$