  The feedback sum-rate capacity is established for the symmetric $J$-user
Gaussian multiple-access channel (GMAC). The main contribution is a converse
bound that combines the dependence-balance argument of Hekstra and Willems
(1989) with a variant of the factorization of a convex envelope of Geng and
Nair (2014). The converse bound matches the achievable sum-rate of the
Fourier-Modulated Estimate Correction strategy of Kramer (2002).
