... ψ :[0,∞) ® [0, ∞) continuous, nondecreas-ing, positive in (0, ∞) and ψ(0) = 0, and byJthe class of functions : [0, ∞) ® [0, ∞)continuous, nondecreasing, and satisfying thatI −ϕ∈F,whereI ... :[0,∞) ® [0, ∞)isacontinuous and nondecreasing function. Moreover, ψ( u)=u - j (u)=u - arctg u isalso continuous and nondecreasing and satisfies ψ(u)>0foru > 0 and ψ(0) = 0. Con-sequently,φ∈J.Caballero ... tgβ1+tgα · tgβ and, asα, β ∈ [0,π2), then tga, tgb Î [0, ∞), we can obtaintg(α − β)≤ tgα − tgβ.Applying j to t he last inequality and taking into account the nondecreasing charac-ter...