Some problems for linear partial differential equations with constant coefficients in the entire space and for a class of degenerate equations in a halfspace

In the space $\mathbf R^{n+1}=\mathbf R_t^1\times\mathbf R_x^n$ we consider a linear partial differential equation with constant coefficients which is solvable in the leading derivative with respect to $t$. We prove that two problems with limit conditions as $t\to-\infty$ which are imposed on the Fourier transform $F_{x\to\sigma}[u(t,x)]$ and contain weight factors, are uniquely solvable in the class of functions $u(t,x)$ which for every $t$ belong to $L_2(\mathbf R_x^n)$ along with the derivatives appearing in the equation and which grow at an order no faster that $t$ as $t\to+\infty$ (in $L_2$). We apply these results to a class of equations in a halfspace which degenerate on the boundary hyperplane.
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