The proton and the photon, who is probing whom in electroproduction?

Abstract

The latest results on the structure of the proton and the photon as seen at HERA are reviewed while discussing the question posed in the title of the talk.Comment: 18 pages, including 28 figures. To be published in the proceedings of the 2nd KEK-Tanashi International Symposium on Hadron and Nuclear Physics with Electromagnetic Probes, KEK-Tanashi, Tokyo, Japan, October 25-27, 1999. Typos in eqs (8) and (9) corrected and reference 5 update