On the nonexistence of a relation between σ-left-porosity and σ-right-porosity

Given an arbitrarily weak notion of left- 〈 f 〉 -porosity and an arbitrarily strong notion of right- 〈 g 〉 -porosity, we construct an example of closed subset of R which is not σ-left- 〈 f 〉 -porous and is right- 〈 g 〉 -porous. We also briefly summarize the relations between three different definitions of porosity controlled by a function; we then observe that our construction gives the example for any combination of these definitions of left-porosity and right-porosity.