I spotted this bicycle during my recent travels. As you can see, it has two power system, the pedals and a small engine:
Engine and pedal powered bicycle.
Note that tiny engine mounted on the frame. Here’s a closer look:
Closer look at the engine on this bicycle.
There’s a separate chain and rear gear there. Take a look at the other side.
Another look at the drive train on this dual powered bicycle.
Not sure how powerful that engine is. However, it has to be helpful on the hills. Quite an interesting contraption. Would like to see it run.