Dual drive is quite simple: 10 cog cassette driver with a 3 speed internal gear hub combined..

leave the hub shifter in 1 gear and you have a 1 by 10..


Complicated was my 3 by 3 by 3 .. 3 cubed, 27 speed; a 3 speed hub, 3 cog cluster and triple crank ..

that was circa 1958.