“…(B.13)We now infer from (B.5) thatb 11 (u)∂ x ϕ 1 ∂ x ϕ 1,+ = b 11 (u)1 (−∞,0) (u 1 )|∂ x u 1 | 2 ≥ 0 , b 12 (u)∂ x ϕ 2 ∂ x ϕ 1,+ = b 12 (u)1 (−∞,0) (u 1 )∂ x u 1 ∂ x u 2 = 0 , b 21 (u)∂ x ϕ 1 ∂ x ϕ 2,+ = b 21 (u)1 (−∞,0) (u 2 )∂ x u 1 ∂ x u 2 = 0 , b 22 (u)∂ x ϕ 2 ∂ x ϕ 2,+ = b 22 (u)1 (−∞,0) (u 2 )|∂ x u 2 | 2 ≥ 0 ,so that the second term on the left-hand side of (B.13) is non-negative. Consequently, (B 13). givesΩ |ϕ 1,+ | 2 + |ϕ 2,+ | 2 dx ≤ 0 ,which implies that ϕ 1,+ = ϕ 2,+ = 0 a.e.…”