For any Boolean functions $f$ and $g$, the question whether $R(f\circ g) = \tilde{ \Theta}(R(f)R(g))$, is known as the composition question for the randomized query complexity. Similarly, the composition question for the approximate degree asks whether $\widetilde{ deg}(f\circ g) = \tilde{ \Theta}(\widetilde{ deg}(f)\cdot\widetilde{ deg}(g))$. These questions are two of the most important and well-studied problems, and yet we are far from answering them satisfactorily. It is known that the measures compose if one assumes various properties of the outer function $f$ (or inner function $g$). This paper extends the class of outer functions for which $\text{ R}$ and $\widetilde{ \text{ deg}}$ compose. A recent landmark result (Ben-David and Blais, 2020) showed that $R(f \circ g) = \Omega(noisyR(f)\cdot R(g))$. This implies that composition holds whenever $noisyR(f) = \Tilde{ \Theta}(R(f))$. We show two results: (1)When $R(f) = \Theta(n)$, then $noisyR(f) = \Theta(R(f))$. (2) If $\text{ R}$ composes with respect to an outer function, then $\text{ noisyR}$ also composes with respect to the same outer function. On the other hand, no result of the type $\widetilde{ deg}(f \circ g) = \Omega(M(f) \cdot \widetilde{ deg}(g))$ (for some non-trivial complexity measure $M(\cdot)$) was known to the best of our knowledge. We prove that $\widetilde{ deg}(f\circ g) = \widetilde{ \Omega}(\sqrt{ bs(f)} \cdot \widetilde{ deg}(g)),$ where $bs(f)$ is the block sensitivity of $f$. This implies that $\widetilde{ \text{ deg}}$ composes when $\widetilde{ \text{ deg}}(f)$ is asymptotically equal to $\sqrt{ \text{ bs}(f)}$. It is already known that both $\text{ R}$ and $\widetilde{ \text{ deg}}$ compose when the outer function is symmetric. We also extend these results to weaker notions of symmetry with respect to the outer function.
Categories: cs.CC