A comparison of two notions of porosity

In the paper we compare two notions of porosity: the R-ball porosity $(R\text{rt}0)$ defined by Preiss and Zajı́ček, and the porosity which was introduced by Olevskii (here it will be called the O-porosity). We find this comparison interesting since in the literature there are two similar results concerning these two notions. We restrict our discussion to normed linear spaces since the R-ball porosity was originally defined in such spaces.