This question comes from my notes, thus slightly unusual structure.
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
.
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 the equality in the middle use
(*) A \otimes [B=>B] ==== [[A=>B] => B]
This funny-looking formula is true for B = G
m
and goes, in that case, under the name of classical locally compact abelian duality (in particular, it exchanges discrete <--> compact
things).
Now I'm somewhat fascinated by the simplicity of (*)
, thus the
Question: Could
(*)
be also true (or perhaps true in some other) sense for (some)B
not necessarilyG
m
?
(Note that would be true if we could write [X => Y] = X
*
\otimes Y
, in analogy with vector spaces, but it's probably too crazy to be a real idea.)