The Effective Lagrangian of QED with a Magnetic Charge
  The effective Lagrangian of QED coupled to dyons is calculated. The resulting generalization of the Euler-Heisenberg Lagrangian contains non-linear $P$- and $T$-nonivariant (but $C$ invariant) terms corresponding to the virtual pair creation of dyons. As examples, the amplitudes for photon splitting and photon coalescence are calculated. 
V. G. Kovalevich (Minsk), P. Osland (Bergen), Ya. M. Shnir (Berlin),   E. A. Tolkachev (Minsk)