A theorem of Hardy states
that, if f is a function on ℝ such that |f(x)|≤ C e−α|x|2 for all x in ℝ and
|f(ξ)|≤ C e−β|ξ|2 for all ξ in ℝ, where α > 0, β > 0, and αβ > 1∕4, then
f = 0. Sitaram and Sundari generalised this theorem to semisimple groups
with one conjugacy class of Cartan subgroups and to the K-invariant case
for general semisimple groups. We extend the theorem to all semisimple
groups.