Large solution-free sets via combinatorial degenerations

Consider the linear form $L(x,y,z,w) = 3x+y-2z-2w$. For a positive integer $N$, denote by $r_L(N)$ the largest size of a subset of $\{1,2,\dots,N\}$ that avoids nontrivial solutions to $L = 0$. We show that $r_L(N) = Ω(N^{0.5608687})$, improving the lower bound for Problem 16 in Green's list of open