code: func (e *FwdEdge) Back(c context.Context) (*BackDepGroup, *BackDep) {
  	bdg := &BackDepGroup{Dependee: *e.To}
  	return bdg, &BackDep{
  		DependeeGroup: ds.KeyForObj(c, bdg),
  		Depender:      *e.From,
  	}
  }
docs: // Back returns the BackDepGroup (To) and the BackDep (From) models that
  // represent the reverse dependency for this FwdEdge.