“…It is easy to check that if b ij = γδ ij , (δ denotes the Kronecker symbol), setting d(x) = |x − x 0 | 2 for any x 0 ∈ R N \Ω, then eventually modifying d as in [11], we see that (1.11) is satisfied; in this case, 13) which is the usual portion of the boundary that arises in the framework of the multiplier method [17,21,34]. We also note that the constraints on the coefficients b ij are almost necessary in order to establish the Carleman estimates needed in the development of our proof method; without these constraints, establishing those estimates would in most cases be impossible as shown in [24].…”