“…For this equation preliminary convergence results can be found in [1], [2], [5], [14] and [33]. Our strongly elliptic systems with convolutional principal part contain, in addition, systems of integro-differential equations [3] (see [7]) with constant coefficients, certain singular integral equations, in particular, those of plane elasticity [7,Appendix], [24], [25], [26], [34], Fredholm integral equations of the second kind [6], [8], [11], [12], [13], [17], [27], [35], and also the integro-differential operator of Prandtl's wing theory [16], [17], [18], [24], [35].…”