A density version of quaternary Goldbach problem

Xiaoyang Hu, Meng Gao

Let $\mathcal{P}$ denote the set of all primes, and let $\underline{\hat{I}}´(P)$ denote the relative lower density of a subset $P$ in $\mathcal{P}$. Suppose that $P_1,P_2,P_3,P_4$ are…