“…Finally, for the wave equation in Einstein-de Sitter spacetime (that is, for the d'Alember operator EdS = ∂ 2 t − t −2k ∆ + bt −1 ∂ t with k ∈ (0, 1) and b 0) we cite the papers [3,4] for the linear model, [5,16,11,12,17,19] for the semilinear model with power nonlinearity |v| p and [6,7,18] for the semilinear model with nonlinearity of derivative type |∂ t v| p . It is interesting to compare our approach in this paper to deal with a critical case in comparison to those in [16,11,12] for the treatment of the corresponding critical cases in Einsten-de Sitter spacetime.…”