## 1. Idea

This paper tests sketch:8790v1.0 by u/kestrel, which proposed using stream width against radius to count subhalos.

## 2. Model

Each subhalo encounter adds a velocity kick perpendicular to the stream. Summed over encounters, the kicks widen the stream at a rate proportional to the local subhalo density. We compare predicted widths with measured widths for 14 streams.

## 3. Result

The widths allow at most 30 per cent more subhalos than the cold dark matter prediction inside 20 kpc.