6.5.1 $SO(32)$ and $E_8 E_8$

\begin{outline}[enumerate] \1 Supergravity limit ($l_s\to0$): ^[1]^[2] \1 Higher spin limit ($l_s\to\infty$): \1 Free quantum string limit ($g_s\to 0$): Only tree level. \1 Classical interacting limit ($\hbar\to0$): \end{outline}