\begin{align} \label{reg_base}
    \Delta lnGDPpc_{i,t} = & \alpha_{i,t} + \beta_{1}lnSLR_{i,t}+ \beta_{2}lnSLR_{i,t}^{2}  + \beta_{3}((x_{i,t} - \omega_{i}(\xi_{i}))^{2}  + \theta lnGDPpc_{i,t-10} + \epsilon_{it}
\end{align}
