code: @Override
      public List<Statement> expand(Term degradation) {
          List<Statement> statements = new ArrayList<Statement>();
  
          BELObject firstArgument = degradation.getFunctionArguments().get(0);
          Term protein = (Term) firstArgument; // only argument of a protein
                                               // degradation term is the protein
  
          // Protein degradation term connects to its protein with
          // DIRECTLY_DECREASES relationship
          final Object obj = new Object(protein);
          Statement statement =
                  new Statement(degradation, null, null, obj, DIRECTLY_DECREASES);
          attachExpansionRuleCitation(statement);
          statements.add(statement);
  
          return statements;
      }
docs: {@inheritDoc}