Let G be a locally compact
group. The notion of “totally real” unitary representation of G is defined
and investigated in §1. In particular, if K is a compact subgroup of G, it
is shown that every closed G-invariant subspace of L2(G∕K) is spanned
by real-valued functions if, and only if, KgK = Kg−1K for every g ∈ G.
In §2 the coset space X = GlK is specialized to a Riemannian symmetric
space, where the double coset condition is replaced by a simple Weyl group
condition.