We show that hierarchies of differential Schroedinger operators for identical
particles which are separating for the usual (anti-)symmetric tensor product,
are necessarily linear, and offer some speculations on the source of quantum
linearity.Comment: As accepted by Journal of Mathematical Physics. Original title
"Separating multi-particle differential Schroedinger operators for identical
particles are necessarily linear". Some new discussion and references. Main
result unchanged. Uses RevTeX 4, 9 page