Solution
= Solution
For binary length-$n$ <linear codes> $C_2\subseteq C_1$, their <bar product of binary linear codes> is
$$
\boxed{
C_1|C_2
=\{(u,u+v):u\in C_1,\ v\in C_2\}
}.
$$
It is a binary linear code of length $2n$ and dimension $\dim C_1+\dim C_2$.