Derive the Huygens Principle through the mutual energy flow theorem

Absorber theory published in 1945 and 1949 by Wheeler and Feyn-man. In the electromagnetic eld theory, W. J. Welch introduced the reciprocity theorem in 1960. V.H. Rumsey mentioned a method to transform the Lorentz reciprocity theorem to a new formula in 1963. In early of 1987 Shuang-ren Zhao (this author) introduced the mutual energy theorem in frequency domain. In the end of 1987. Adrianus T. de Hoop introduced the time-domain cross-correlation reciprocity theorem. All these theories can be seen as a same theorem in dierent domain: Fourier domain or in time domain. After 30 years silence on this topic, nally, this author has introduced the mutual energy principle and self-energy principle which updated the Maxwell's electromagnetic eld theory and Schrödinger's quantum mechanics. According to the theory of mutual energy principle, the energy of all particles are transferred through the mutual energy ows. The mutual energy ow are inner product of the retarded wave and the advanced wave. The mutual energy ow satises the mutual energy ow theorem. The retarded wave is the action the emitter gives to the absorber. The advanced wave is the reaction the absorber gives to the emitter. In this article this author will derive the Huygens principle from the mutual energy ow theorem. The bra, ket and the unit operator of the quantum mechanics will be applied to the inner space dened on 2D surface instead of the 3D volume