Isotropic Forms of Dynamics in the Relativistic Direct Interaction   Theory
  The Lagrangian relativistic direct interaction theory in the various forms of dynamics is formulated and its connections with the Fokker-type action theory and with the constrained Hamiltonian mechanics are established. The motion of classical two-particle system with relativistic direct interaction is analysed within the framework of isotropic forms of dynamics in the two- and four-dimensional space-time. Some relativistic exactly solvable quantum-mechanical models are also discussed. 
A. Duviryak, V. Shpytko, V. Tretyak (Institute for Condensed Matter   Physics)