def on_term(term_node)
      if defined? @separate_by_comma
        remove_instance_variable(:@separate_by_comma)
      end
      process(term_node.function)
      bel_string << '('
      term_node.arguments.each { |arg| process(arg) }
      bel_string << ')'
    end
def on_term(term_node)
      if defined? @separate_by_comma
        remove_instance_variable(:@separate_by_comma)
      end
      process(term_node.function)
      bel_string << '('
      term_node.arguments.each { |arg| process(arg) }
      bel_string << ')'
    end
Called when visiting nodes of type +term+.