“…Boundary conditions (2.4) and (2.5) on the fixed boundary ∂B could be interpreted in the sense of traces if the distributions of subsets ∂B N and ∂B D on ∂B were sufficiently regular. To avoid any regularity assumptions with respect to these distributions let us introduce a subspace W 1,2 0 (B, ∂B D ) ⊂ W 1,2 (B) as the closure of the set of smooth functions C ∞ 0 B\∂B D with compact support in B\∂B D . Then condition (2.5) implies that p(•) − P (•) ∈ W 1,2 0 (B, ∂B D ) for some given function P ∈ W 1,2 (B).…”