The homogeneous degree 4 part of $\diamondsuit$ is of the form: $$B_1\circ B_4-z+x+B_2\circ B_3+B_3\circ B_2+B_4\circ B_1+2a_{21}B_1B_2(x,y)z-2a_{12}xB_1B_2(y,z).$$
so there's this meta.stackoverflow.com/questions/185205/… , but when i follow those instructions it won't allow me to select mathoverflow as my parent site, just one of the classical stackexchange sites
