class Sass::Value::Number

def unit_string(numerator_units, denominator_units)
  if numerator_units.empty?
    return 'no units' if denominator_units.empty?
    return denominator_units.length == 1 ? "#{denominator_units.first}^-1" : "(#{denominator_units.join('*')})^-1"
  end
  return numerator_units.join('*') if denominator_units.empty?
  "#{numerator_units.join('*')}/#{denominator_units.join('*')}"
end