Porosity and regularity in metric measure spaces

This is a report of a joint work with E. J"arvenp"a"a, M. J"arvenp"a"a, T. Rajala, S. Rogovin, and V. Suomala. In [3], we characterized uniformly porous sets in $s$-regular metric spaces in terms of regular sets by verifying that a set $A$ is uniformly porous if and only if there is $t<s$ and a $t$-regular set $F\supset A$. Here we outline the main idea of the proof and also present an alternative proof for the crucial lemma needed in the proof of the result.