Finally, the log propagator propagates the change to all indices. This is the mathematically precise form of the relativistic particle propagator, free of any ambiguities. The solid lines correspond to a fermion propagator, the wavy lines to bosons. The vertices might be connected by a bosonic or fermionic propagator. The propagator for the spin-1 fields has the usual Feynman form. A state space with a distinguished propagator is also called a dynamical system. The propagator is still the inverse of the quadratic part. In this gauge, the Feynman diagrams are constructed from a single propagator and vertex. He is popularly seen as a propagator and reviver of Jainism. The Feynman propagator has some properties that seem baffling at first. The second term is the free particle propagator, corresponding to times a diffusion process. The propagator typically has singularities on the mass shell. The Dyson equation relates the full propagator, the bare propagator and the 1PI self-energy. A contour going clockwise over both poles gives the causal retarded propagator. A contour going anti-clockwise under both poles gives the causal advanced propagator.