“…Further sharp decoupling inequalities for (non-degenerate) quadratic d-surfaces of co-dimension 2 were proven, for 2 ď d ď 4, in [DGS19] and [GZ20a]. More recently, in [GORYZ19], the classification of sharp decoupling inequalities for quadratic 3-surfaces in R 5 was completed, and sharp decoupling inequalities were proved in the "degenerate" cases, which were not covered by previously mentioned works. The approach to the "degenerate" cases in [GORYZ19] stands out from the previously mentioned works, in that it relies on small cap decouplings for the parabola and the 2-surface pξ 1 , ξ 2 , ξ 2 1 , ξ 1 ξ 2 q (we refer also to [DGW20] for further discussion of small cap decouplings).…”