  The Newell-Littlewood numbers $N_{\mu,\nu,\lambda}$ are tensor product
multiplicities of Weyl modules for classical Lie groups, in the stable limit.
For which triples of partitions $(\mu,\nu,\lambda)$ does
$N_{\mu,\nu,\lambda}>0$ hold? The Littlewood-Richardson coefficient case is
solved by the Horn inequalities (in work of A. Klyachko and A. Knutson-T. Tao).
We extend these celebrated linear inequalities to a much larger family,
suggesting a general solution.
