Could you please explain to me what is meant by the notation : $ \mathrm{ad} $ that appears on the following link : www.jmilne.org/math/xnotes/tc.pdf in the middle of the page : $ 36 $.
The level required to tackle this course on the link above is quite high. But the notation in question is part of the field of sesqui-linear algebra.
Thanks in advance for your help.
From what I have seen of Lie algebra theory, I would guess that $\text{ad}(c)$ refers to the operator $a\mapsto [c,a]$, i.e. taking the commutator with $c$.