Definition 2.8
(Spectrum)
.
Let
1
≥
ρ
>
0
and
f
:
G
→
ℂ
. Define the
ρ
-large
spectrum of
f
to be
Spec
ρ
(
f
)
=
{
γ
∈
G
^
:
|
f
^
(
γ
)
|
≥
ρ
∥
f
∥
1
}
.