operator does not have a momentum flowing out of the operator itself. If there is a net momenta flow through the operator then they mix into a set of total derivative operators. Given that the RI${}^\prime$/SMOM scheme is at non-exceptional momenta then this mixing cannot be ignored. It has been studied to three loops in a practical situation in [@36] where a similar problem for the lattice was examined but in a context which involves a Green’s function which is gauge independent but contains two operators. Indeed the mixing matrix for the two Wilson operators we consider here was calculated to three loops in the ${\overline{\mbox{MS}}}$ scheme. Without including the mixing in [@36] the operator correlation function did not correctly satisfy the renormalization group equation at two and three loops.

The article is organised as follows. We review the problem and the necessary background in the following section. All our results are collected in sections three and four where we give all the amplitudes as a function of the gauge parameter of an arbitrary linear covariant gauge for both the ${\overline{\mbox{MS}}}$ and RI${}^\prime$/SMOM schemes. We conclude in section five and include an appendix. It contains the bases of tensors into 