Let's use the notation of [A=>B]
for Hom(A, B)
. Take a 1-dimensional algebraic torus G
m
and higher-dimensional torus T
and let's live in the category of commutative algebraic groups over k
.
Out of four expressions like [G
m
=> [G
m
=>T]]
etc. half give back T
(*)
, others the dual torus T
V
, in the sense that X
*
(T) :=
[G
m
=> T] = [T
V
=> G
m
] =: X
*
(T
V
)
.
To prove equality (*)
use for B = G
m
(**) A \otimes [B=>B] ==== [[A=>B] => B].
Question: Is there an example of commutative algebraic group
B
, other thanG
m
, for which the identity(**)
is also true or perhaps true in some other sense?
(One thing I specifically have in mind is that if we could write [X => Y] = X
*
\otimes Y
whenever X
and Y
are groups, as if it was a with any rigid tensor category, the formula would hold for all A
and B
)