Mathematically, the reciprocal lattice is the set of all vectors G m , that are wavevectors of plane waves in the Fourier series of a spatial function whose periodicity is the same as that of a direct lattice as the set of all direct lattice point position vectors R n , and G m satisfy this equality for all R n . Each plane wave in the Fourier series has the same phase (actually can be differed by a multiple of 2 π π ) at all the lattice point R n .