Although not truly fundamental, the residual strong force shared by nucleons can also be r...

Although not truly fundamental, the residual strong force shared by nucleons can also be represented by a Feynman diagram, with the pion filling the role of mediating boson. The accompanying diagram represents a force between a neutron and a proton mediated by a π° boson. Suggest a diagram in which they exchange a π- particle. (We demand that there be a neutron and a proton only at the start and finish.)