Solution
= Solution
Substituting $J_m=\epsilon_{mij}M^{ij}/2$ and $K_i=M^{0i}$ yields
$$
\boxed{
[K_i,K_j]=-\epsilon_{ijk}J_k,\qquad
[J_i,K_j]=\epsilon_{ijk}K_k,\qquad
[J_i,J_j]=\epsilon_{ijk}J_k}.
$$
= Solution
Substituting $J_m=\epsilon_{mij}M^{ij}/2$ and $K_i=M^{0i}$ yields
$$
\boxed{
[K_i,K_j]=-\epsilon_{ijk}J_k,\qquad
[J_i,K_j]=\epsilon_{ijk}K_k,\qquad
[J_i,J_j]=\epsilon_{ijk}J_k}.
$$