Offspring-bounded labels without a third moment

The two-walk truncation follows the argument in the supplied preprint OpenAI211 (Section 5). It uses ${\mathbb{E}}_{\mathrm{sp}}K=\mathbb{E}{\xi }^2$, not ${\mathbb{E}}_{\mathrm{sp}}{K}^2=\mathbb{E}{\xi }^3$. An exponential moment or a third offspring moment is not silently introduced.