As shown in the section multi-dimensional Fourier series, G m can be chosen in the form of G m = m 1 b 1 + m 2 b 2 + m 3 b 3 where a i ⋅ ⋅ b j = 2 π π δ δ i j . With this form, the reciprocal lattice as the set of all wavevectors G m for the Fourier series of a spatial function which periodicity follows R n , is itself a Bravais lattice as it is formed by integer combinations of its own primitive translation vectors ( b 1 , b 2 , b 3 ) , and the reciprocal of the reciprocal lattice is the original lattice, which reveals the Pontryagin duality of their respective vector spaces. (There may be other form of G m . Any valid form of G m results in the same reciprocal lattice.)