Geodesic
On smooth solutions of a class of almost hypoelliptic equations of constant strength
Eurasian mathematical journal, Tome 10 (2019) no. 4, pp. 92-95.

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In this paper we state a new theorem about smoothness of solutions of almost hypoelliptic and hypoelliptic by Burenkov equation $P(x',D)u=0$, where the coefficients of the linear differential operator $P(x, D) = P(x_1,\dots, x_n, D_1,\dots, D_n)$ of uniformly constant strength depend only on the variables $x' = (x_1,\dots, x_k)$, $k \leqslant n$: if the operator $P(x', D)$ is hypoelliptic by Burenkov and almost hypoelliptic for any $x'\in\mathbb{E}^k$, then all the solutions of the differential equation $P(x', D)u = 0$ belonging to a certain weighted Sobolev class are infinitely differentiable functions. 
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H. G. Ghazaryan; V. N. Margaryan. On smooth solutions of a class of almost hypoelliptic equations of constant strength. Eurasian mathematical journal, Tome 10 (2019) no. 4, pp. 92-95. http://geodesic.mathdoc.fr/item/EMJ_2019_10_4_a9/

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