By Lemma 2 we have are continuous on D × G ′ . for 0 ≤ ∣ $_{β}$′ ∣ ≤ 2, 1 ≤ j ≤ n . Thus it follows from equalities (4.7), (A.14) and (A.15) that ∂ β ′ ξ ′ ϝ $_{2}$, ∂ β ′ ξ ′ ∂$_{x}$$_{j}$ ϝ 2 ∈ C ( D × Δ 1 η × $_{G}$′ ) ∩ L$_{2}$ ( Δ 1 η ) , (A.15) d dτ ζ k = − 2 n ∑ j =2 Γ k 1 $_{j}$ζ$^{j}$, 2 ≤ k ≤ n the integrals where x 1 0 is the first component of the boundary point ( x 1 $_{0}$, x ′ ) ∈ ∂D and the first component of ( x $^{1}$, x ′ ) ∈ D satisfies x 1 > x 1 $_{0}$. In (A.16), the components of the vector $_{ζ}$′$_{(}$$_{τ , ξ}$ ′$_{) = (}$$_{ζ}$ $^{2}$( $_{τ , ξ}$′$_{)}$$_{, ..., ζ}$ $^{n}$( $_{τ , ξ}$′$_{)) satisfy the system of differential equations}$ 2 π ∫ + ∞ −∞ u $^{2}$( x, ξ ) dξ 1 = ∫ + ∞ −∞ ∣ ̂ u ( $_{x, η, ξ}$′$_{)}$ ∣ 2 dη, ∫ + ∞ 0 q $^{2}$( $_{x, η, ξ}$′$_{)}$$_{dη,}$ ∫ + ∞ 0 p $^{2}$( $_{x, η, ξ}$′$_{)}$$_{dη}$ 23