Help me clean this up so one scope uses the other!

article.rb

# I have this AR model that has two scopes that should return complementary sets
# of rows: one returns all the rows that match certain conditions, the other
# returns all rows that DON'T match the same conditions.
#
# I would like to build the second scope using the first one. Something like:
#
#     class Article
#       def self.problematic
#         not(complete)
#       end
#     end
#
# For now the conditions are simple enough (just check for NULL/NOT NULL), but
# it's probable that I might need some more complex conditions in the future
# (like published_on < Time.current, since our scraper sometimes messes up).
#
# So this scope will become more complex, and I would like to avoid having to
# duplicate all the logic between both scopes.
#
# After poking around ARel's source code for a while I didn't find an easy way
# to do this. How would you approach this?

class Article < ActiveRecord::Base
  @attributes_required_for_complete = [:published_on, :title, :text, :url]

  # Public: Filter out articles that don't have all the information required for
  # us to show to users.
  #
  # Returns an ActiveRecord::Relation.
  def self.complete
    @attributes_required_for_complete.inject(self) do |relation, field|
      relation.where("#{field} IS NOT NULL")
    end
  end

  # Public: Filter articles that don't have all the information required for us
  # to show to users. This returns the complement of Article.complete.
  #
  # Returns an ActiveRecord::Relation.
  def self.problematic
    conditions = @attributes_required_for_complete.map do |field|
      arel_table[field].eq(nil)
    end
    where(conditions.inject(:or))
  end
end