In relativistic quantum mechanics and quantum field theory the propagators are Lorentz invariant. Feynman diagrams with more than one loop always contain internal boson propagators. In the homogeneous case the propagators are exponentials of the Hamiltonian. There are a number of possible propagators for free scalar field theory. In quantum mechanics, the propagators are usually unitary operators on a Hilbert space. The propagators can be expressed as time-ordered exponentials of the integrated Hamiltonian. Common to all thermodynamic cycles the consecutive segment propagators do not commute formula 28. Horticultural tissue culture may also be utilized by propagators with the appropriate equipment. Interesting physics, as propagators and effective couplings for interactions, can be straightforwardly extracted from it. In quantum field theory, Green's functions take the roles of propagators. He was one of the first propagators of devangism. They follow Jainism, the religion taught by the twenty-four propagators of faith called "tirthankaras". Erich Obst was one of the propagators during World War II. These take a much simpler form than the position space propagators. Commuting propagators will lead to zero power.