& \sqrt{N}(q-0) \xrightarrow{d} \mathcal{N} \left(0, \begin{bmatrix}1 & -1 \end{bmatrix} \begin{bmatrix} \operatorname{Var}(b_1) & \operatorname{Cov}(b_1,b_0) \\ \operatorname{Cov}(b_1,b_0) & \operatorname{Var}(b_{0}) \end{bmatrix}\begin{bmatrix} 1 \\ -1 \end{bmatrix}\right) \\[6pt]
