“…We can find it, for example, in Ue and Wang, Grasselli and Pata, and Robinson. 4,14,15 For 1 3 , and H k 0 (Ω) = (H k 0 (Ω)) 3 will denote the Lebesgue and Sobolev spaces of vector-valued functions on Ω as usual, where H k = W k,2 is a Hilbert space. We also denote by ||.|| and ⟨•, •⟩ the normal and scalar product in L 2 (Ω), respectively.…”