Let the source alphabet be A = {a_1, a_2, ? ? ? , a_n}, each source symbol a_i having probability p_i \ge 0,\Sigma _{i = 1}^n pi = 1. Let the encoding alphabet be \Sigma = {\alpha1 ,\alpha2, ? ? ? , \alpha_r}, where each letter a_i has an integer cost c_i, such that 0 \le c_1 \le c_2 \le?? ? \le c_r = C, and the greatest common divisor of all costs is 1.