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Classical and quantum mechanics of relativistic particles

It is shown that the standard actions of relativistic point-like particles are adapted within the corresponding interpretation to describe particle and antiparticle at the same time. The special gauge in which this possibility is realised both in classical and in quantum theory is pointed out. A consistent procedure of canonical quantisation of a relativistic point-like particle with and without spin is considered. The operator formulation of the system in question is manifestly constructed. Quantum mechanics constructed in this way proves to be equivalent, for a spinless particle, to Klein-Gordon theory and for a spinning particle to Dirac theory.