Zelevinsky's mutual-position conjecture for multisegment multiplicities

Let $\Pi$ be a cuspidal support, let $\mathcal{O}(\Pi)$ denote the corresponding Zelevinsky line, and let $\mathbf{a}$ and $\mathbf{b}$ be multisegments belonging to the same $\mathcal{O}(\Pi)$. Write $m(\mathbf{b},\mathbf{a})$ for the multiplicity of $L_{\mathbf{b}}$ in $\pi(\mathbf{a})$. Zelevinsky's mutual-position conjecture. The coefficient $m(\mathbf{b},\mathbf{a})$ depends only on the mutual relation between $\mathbf{a}$ and $\mathbf{b}$. The paper identifies this as a conjecture due to Zelevinsky and states that its main symmetrization result proves it.