begin{feynman}
    vertex (v1) {(cl)};
    vertex[right=0.5cm of v1] (v2) {(cl)};
    vertex[right=1cm of v2] (v3) {(cl)};
    vertex[right=0.5cm of v3] (v4) {(cl)};;
    diagram*{(v1)--(v2), (v2)--[half left](v3)--[half left](v2),(v3)--(v4)};
end{feynman}

begin{feynman}
        vertex (v1);
        vertex[right=0.5cm of v1] (v2);
        vertex[right=1cm of v2] (v3);
        vertex[right=0.5cm of v3] (v4);
        diagram*{(v1)--[edge label={(cl quad)}](v2), (v2)--[half left,edge label={(cl quad cl)}](v3)--[half left,edge label={(cl quad cl)}](v2),(v3)--[edge label={(quad cl)}](v4)};
    end{feynman}