$[v_4,l_4]=$?, where v_4 $v_4$ is the Hopf map in \pi_7(S^4) $\pi_7(S^4)$ and l_4 $l_4$ is the generator of \pi_4(S^4) $\pi_4(S^4)$ which represent the identity map, [,] $[,]$ is whitehead product.