code: private void deleteRemainingRelationsFromMatrix(IMappingElement<INode> e) {
          //deletes all the relations in the column
          for (INode i : defautlMappings.getSourceContext().getNodesList()) {
              if (i != e.getSource()) {
                  defautlMappings.setRelation(i, e.getTarget(), IMappingElement.IDK);
              }
          }
  
          //deletes all the relations in the row
          for (INode j : defautlMappings.getTargetContext().getNodesList()) {
              if (j != e.getTarget()) {
                  defautlMappings.setRelation(e.getSource(), j, IMappingElement.IDK);
              }
          }
      }
docs: When a given mapping element has been chosen as the strongest,
  then delete all the other mappings from the temp by
  setting the relation to <code>null</code>.
  
  @param e the strongest mapping element.