  We prove that the 3-manifold obtained by gluing the complements of two
nontrivial knots in homology 3-sphere instanton L-spaces, by a map which
identifies meridians with Seifert longitudes, cannot be an instanton L-space.
This recovers the recent theorem of Lidman, Pinzon-Caicedo, and Zentner that
the fundamental group of every closed, oriented, toroidal 3-manifold admits a
nontrivial SU(2)-representation, and consequently Zentner's earlier result that
the fundamental group of every closed, oriented 3-manifold besides the 3-sphere
admits a nontrivial SL(2,C)-representation.
