  Let $A(n,d)$ (respectively $A(n,d,w)$) be the maximum possible number of
codewords in a binary code (respectively binary constant-weight $w$ code) of
length $n$ and minimum Hamming distance at least $d$. By adding new linear
constraints to Schrijver's semidefinite programming bound, which is obtained
from block-diagonalising the Terwilliger algebra of the Hamming cube, we obtain
two new upper bounds on $A(n,d)$, namely $A(18,8) \leq 71$ and $A(19,8) \leq
131$. Twenty three new upper bounds on $A(n,d,w)$ for $n \leq 28$ are also
obtained by a similar way.
