((∑_(m=-(Subscript[N, pre]))^(N+(Subscript[N, post])-1))(x^l)[m]w[m](e^((j 2 π mk)/N))=(∑_(m=-(Subscript[N, pre]))^(-1))(x^l)[m]w[m](e^(-((j 2 π mk)/N)))+(∑_(k=0)^(N-1))(x^l)[m]w[m](e^(-((j 2 π mk)/N)))+(∑_(m=N)^(N+(Subscript[N, post])-1))(x^l)[m]w[m](e^(-((j 2 π mk)/N)))Equation   (18))