“…The differential operator p + q is known as the (p, q)-Laplacian operator, if p = q, where j , j > 1 denotes the j-Laplacian defined by j u := div(|∇u| j-2 ∇u). It is not homogeneous, thus some technical difficulties arise in applying the usual methods of the theory of elliptic equations (for further details, see [1,2,5,7,8,10,[12][13][14][15][16][19][20][21][22][23] and references therein).…”