Solution
= Solution
With all momenta incoming, the <Feynman rules> are
$$
\text{propagator: }\frac{i}{p^2-m^2+i\epsilon},
$$
$$
\text{three-point vertex: }
2i\lambda\sum_{j=1}^3(p_j^2-m^2),
$$
and
$$
\text{four-point vertex: }
4i\lambda^2\left(\sum_{j=1}^4p_j^2-3m^2\right).
$$
Each vertex includes its momentum-conserving delta function. The combinatorial factors follow by assigning the identical fields to the differentiated and undifferentiated slots in every possible way.