Why are there two air fuel ratio sensors on the Audi A1?

I noticed that my Audi A1 has two air fuel ratio sensors instead of just one like most cars. Is there a specific reason for this design, and how do the sensors work together to optimize fuel efficiency?

The reason for having two air fuel ratio sensors on the Audi A1 is to ensure more accurate readings and better engine performance. One sensor monitors the air-fuel mixture before the catalytic converter, while the other monitors it after. This allows the engine control unit to make more informed adjustments for optimal fuel efficiency.