  In this paper, we consider the Reed-Muller (RM) codes. For the first order RM
code, we prove that it is unique in the sense that any linear code with the
same length, dimension and minimum distance must be the first order RM code;
For the second order RM code, we give a constructive linear sub-code family for
the case when m is even. This is an extension of Corollary 17 of Ch. 15 in the
coding book by MacWilliams and Sloane. Furthermore, we show that the specified
sub-codes of length <= 256 have minimum distance equal to the upper bound or
the best known lower bound for all linear codes of the same length and
dimension. As another interesting result, we derive an additive commutative
group of the symplectic matrices with full rank.
