# File lib/active_ldap/distinguished_name.rb, line 189
    def -(other)
      rdns = @rdns.dup
      normalized_rdns = normalize(@rdns)
      normalize(other.rdns).reverse_each do |rdn|
        if rdn == normalized_rdns.pop
          rdns.pop
        else
          raise ArgumentError, _("%s isn't sub DN of %s") % [other, self]
        end
      end
      self.class.new(*rdns)
    end