def -(other)
      records = @records.clone.reject { |name, records| other.records.include?(name) }
      SearchAtom.new(records)
    end
def -(other)
      records = @records.clone.reject { |name, records| other.records.include?(name) }
      SearchAtom.new(records)
    end
Creates a new SearchAtom with records in other removed from self.