}
	selectingObject := m.selectingObjects[key]
	selectorKey := selectingObject.selectorKey
	defer delete(m.selectingObjects, key)
	if _, ok := m.labeledBySelecting[selectorKey]; !ok {
		// No associations.
		return
	}
	// Remove associations.
	for _, labeledObject := range m.labeledBySelecting[selectorKey].objects {
		labelsKey := labeledObject.labelsKey
		// Delete labeledObject to selectingObject association.

func emptyMap(m *BiMultimap) error {
	if len(m.labeledObjects) != 0 {
		return fmt.Errorf("Found %v labeledObjects. Wanted none.", len(m.labeledObjects))
	}
	if len(m.selectingObjects) != 0 {
		return fmt.Errorf("Found %v selectingObjects. Wanted none.", len(m.selectingObjects))
	}
	if len(m.labeledBySelecting) != 0 {
		return fmt.Errorf("Found %v cached labeledBySelecting associations. Wanted none.", len(m.labeledBySelecting))
	}