Mathematical analysis. -Local clustering of the non-zero set of functions in W 1,1 (E), by EMMANUELE DIBENEDETTO, UGO GIANAZZA and VINCENZO VESPRI.ABSTRACT. -We extend to the p = 1 case a measure-theoretic lemma previously proved by DiBenedetto and Vespri for functions u ∈ W 1,p (K ρ ) where K ρ is an N -dimensional cube of edge ρ. It states that if the set where u is bounded away from zero occupies a sizeable portion of K ρ , then the set where u is positive clusters about at least one point of K ρ .