Solution
= Solution
The momentum-space <Feynman rules> for <Phi cubed theory> are
$$
\text{internal scalar line: }\frac{i}{p^2-m^2+i\epsilon},
\qquad
\text{cubic vertex: }-ig.
$$
Each vertex carries $(2\pi)^4\delta^{(4)}$ of momentum conservation, each independent loop momentum is integrated with $d^4\ell/(2\pi)^4$, and a graph is divided by its <Feynman-diagram symmetry factor>. External propagators are omitted from an amputated <scattering amplitude>.