@Article{ BatSpe11, author = { Bate, David and Speight, Gareth }, title = { Differentiability, Porosity and Doubling in Metric Measure Spaces }, journal = { Proceedings of the American Mathematical Society }, year = { 2011 }, volume = { 141 (2013) }, pages = { 971-985 }, URL = { http://cvgmt.sns.it/paper/3439/ }, note = { cvgmt preprint} }