$ (1)$
Find formulas for a three parts Karatsuba's trick. Using MAPLE, for setting up these formulas, would be a good idea.
$ (2)$
Is this three parts Karatsuba's trick theoretically better than the usual two parts one? That is, does this lead to a better time complexity upper bound?
Question $ (2)$ is a bit difficult and requires to study carefully the sections of the Introduction chapter on complexity estimates.

Marc Moreno Maza