Let (H,τ) bc a topological
vector space and let T be a compact linear operator mapping H into H (i.e., T[V ] is
contained in a τ− compact set for some τ− neighborhood V of the zero vector in H).
Sufficient conditions are given for (H,τ) so that T has a non-triviaI, closed invariant
linear subspace. In particular, it is shown that any complete, metrizable topological
vector space with a Schauder basis satisfies the conditions stated in this paper.
The proofs and conditions are stated within the framework of nonstandard
analysis.