“…There are a lot of papers that deal with null controllability for (1.1) when the dispersion coefficient k is a constant or a strictly positive function (see, for example, [3]). If y is independent of a and k degenerates at the boundary or at an interior point of the domain we refer, for example, to [2], [15] and to [17], [18], [19] if µ is singular at the same point of k. To our best knowledge, [1] is the first paper where y depends on t, a and x and the dispersion coefficient k can degenerate. In particular, the authors assume that k degenerates at the boundary (for example k(x) = x α , being x ∈ (0, 1) and α > 0).…”