Mera Rivas, María EugeniaMorán Cabré, ManuelPreiss, DavidZajicek, Ludik2023-06-202023-06-2020030951-7715https://hdl.handle.net/20.500.14352/60449We show that given a σ-finite Borel regular measure μ in a metric space X, every σ-porous subset of X of finite measure can be approximated by strongly porous sets. It follows that every σ-porous set is the union of a σ-strongly porous set and a μ-null set. This answers in the positive the question whether a measure which is absolutely continuous with respect to the σ-ideal of all σ-strongly porous sets is absolutely continuous with respect to the σ-ideal of all σ-porous sets. Using these results, we obtain a natural decomposition of measures according to their upper porosity and obtain detailed information on values that upper porosity may attain almost everywhere.engjournal articlehttps://doi.org/10.1088/0951-7715/16/1/315open accessFísica (Física)Matemáticas (Matemáticas)22 Física12 Matemáticas