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Define the standard perturbation theory velocity kernel bywhere ${\int }_{\mathbf{q}}=\int d^{3}q/(2\pi {)}^3$ and $P(q)=⟨|{\delta }_1(\mathbf{q}){|}^2{⟩}^{\prime }$. For ${\mathbf{k}}_1+{\mathbf{k}}_2+{\mathbf{k}}_3=0$, one representative external labelling of the tree contribution isThe four one-loop representatives areThe full answer adds the distinct permutations of the external labels; the question asks for only one labelling of each topology.