Simplexes in a normed space

Is it true that any set of n + 1 points in Rⁿ can be isometrically embedded into any n-dimensional real normed apace? For n ≥ 3, the answer to this question is unknown to the author of this paper. For n = 2, it is clear that the answer is positive. For n = 3, the problem is reduced to the case where four points lie in a plane. A certain reduction is assigned for arbitrary n.