International workshop on photon-photon collisions. International Workshop on Photon Photon Collisions International Workshop on Photon-Photon Collisions International colloquium on photon-photon interactions International Workshop on Digital Communications International Workshop on Photon-Photon Collisions: Proceedings of the... International workshop on amorphous semiconductors International workshop on aperiodic crystals. International Workshop on Scientific Computing and Applications International congress on photosynthesis