“…u : Q -* R; u is strictly positive in Q; (1)(2)(3) see e. g. [1,2,3,7,8,9,13]; see also [11,17,18,19] for gênerai results about parabolic free-boundary problems and for further références. As pointed out e. g. in [1,2,3,9] (-x) 9 and C/g (je) ^ 1, U' o (x) ^ 0 for x > 0, the solution U satisfies U (-x, t) = U(x 9 t) and U t (x, t) ^0, U x (x 9 t) £0 in the fîrst quadrant Q = { (x, t) \ x > 0, t > 0 }, so that, setting:…”