Karatsuba’s “divide-and-conquer” multiplication algorithm has its roots in a method that Carl Friedrich Gauss (1777-1855) introduced involving the multiplication of complex numbers.

He explains: “State-of-the-art numerical algorithms already exist, such as optimal subsampling algorithms and divide and conquer algorithms ... between the number of the machines and the ...

The point being that the same rules apply whether you’re dividing fractions or whole numbers ... don’t need to flip and multiply fractions in order to divide and conquer them.