Describes a Fourier polynomial
by a list of terms and their coefficients, i.e. for a Fourier polynomial:
p(x) = ∑cα•Χα(x) it holds the mapping of α
to its coefficient cα.
This abstract class is used for describing functions over G -> C where G is Z_N1 x ... x Z_Nk or
alternatively G is a finite Abelian group described by (gj,Nj) j=1,...