  A remarkable feature of Schur functions -- the common eigenfunctions of
cut-and-join operators from $W_\infty$ -- is that they factorize at the
peculiar two-parametric topological locus in the space of time-variables, what
is known as the hook formula for quantum dimensions of representations of
$U_q(SL_N)$ and plays a big role in various applications. This factorization
survives at the level of Macdonald polynomials. We look for its further
generalization to {\it generalized} Macdonald polynomials (GMP), associated in
the same way with the toroidal Ding-Iohara-Miki algebras, which play the
central role in modern studies in Seiberg-Witten-Nekrasov theory. In the
simplest case of the first-coproduct eigenfunctions, where GMP depend on just
two sets of time-variables, we discover a weak factorization -- on a
codimension-one slice of the topological locus, what is already a very
non-trivial property, calling for proof and better understanding.
