“…In fact, most of the research was devoted to the classical solutions. Later, mixed problems with integral conditions for both parabolic and hyperbolic equations were studied by Ionkin [13], Ionkin and Moiseev [14], Kamynin [15], Pulkina [32,33], Volkodavov and Zhukov [36], Yurchuk [37], Kartynnik [16], Muravei and Philinovskii [31], Bouziani [4], Mesloub [19], Mesloub and Bouziani [20][21][22], Mesloub and Messaoudi [24][25][26], Mesloub and Lekrine [23]. We should mention here that the presence of the integral term in the boundary condition can greatly complicate the application of standard functional techniques (see [24,25]).…”