Uniformly rectifiable metric spaces satisfy the weak constant density condition

The weak constant density condition is a quantitative regularity property originally investigated by David and Semmes in their foundational work on uniform rectifiability. Roughly speaking, a space satisfies this condition if in most balls, the space supports a measure with nearly constant density in a neighborhood of scales and locations. In this paper, we prove that uniformly rectifiable metric spaces satisfy the weak constant density condition, extending a theorem of David and Semmes. In order to do this, we first prove a slightly modified version of a separate theorem of David and Semmes which weakly controls the oscillation of the means of L² functions.