inner form

《Naive Lie Theory》 · 第 219 页 · Chapter 12，Section 12.3.7「Forms」

We have a homomorphism $G(F_s) o \operatorname{Aut}_{F_s}(G)$, sending an element to the inner automorphism that it defines, whence a map $\operatorname{Int}$ of $H^1(F,G)$ to $\Phi(F,G)$. An $F$-form of $G$ whose isomorphism class is in the image of $\operatorname{Int}$ is said to be an inner form. A form that is not inner is outer.