Multi-photon production in e+e- collisions at √s=181-209 GeV - Abbiendi, G; Ainsley, C; Åkesson, PF; Alexander, G; Allison, J; Amaral, P; Anagnostou, G; Anderson, KJ; Arcelli, S; Asai, S; Axen, D; Azuelos, G; et al. (EUROPEAN PHYSICAL JOURNAL C, 2003)