Processes of the type proton+proton --> pion+anything at high energy are discussed. The differential cross section for such reactions is expressed in terms of a three-particle --> three-particle amplitude. This amplitude is then expanded into O(2, 1) representations. If the Pomeranchuk trajectory is the dominant O(2, 1) singularity at high energy, the existence of pionization and limiting fragmentation is obtained. Furthermore, the pionization products are essentially independent of the target and projectile, while the fragments of the target are independent of the projectile. Modifications in the presence of strong Regge cuts at J=1 are discussed.