Let $A$ and $B$ be matrices of respective sizes $m \times n$ and $n \times p$.
(a) Prove that $\operatorname{dim} \operatorname{ker}(A B) \leq \operatorname{dim} \operatorname{ker} A+\operatorname{dim} \operatorname{ker} B$.
(b) Prove the Sylvester Inequalities $\operatorname{rank} A+\operatorname{rank} B-n \leq \operatorname{rank}(A B) \leq \min \{\operatorname{rank} A, \operatorname{rank} B\}$.