A Kakeya maximal estimate for regulus strips

We prove Kakeya-type estimates for regulus strips.

As a result, we obtain another epsilon improvement over the Kakeya conjecture in $\mathbb{R}^3$, by showing that the regulus strips in the ${\rm SL}_2$ example are essentially disjoint.

We also establish an $L^p$ inequality regarding Nikodym-type maximal function in the first Heisenberg group.