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“ Par. 64. That if at any time the commission shall be in doubt of the elements of value to be by them considered in arriving at the true valuation under the provisions of this section, they are - authorized and empowered to institute a proceeding in equity in the Supreme Court of the District of Columbia petitioning said court to instruct them as to the element or elements of value to be by them considered as aforesaid, and the particular utility under valuation at the time shall be made party defendant in said action. That any public utility and any person or corporation interest [ed] being dissatisfied with any order or ‘decision of the' commission fixing *439any valuation, rate or rates, tolls, charges, schedules, joint rate or rates, or regulation, requirement, act, service or other thing com-' plained of may commence a proceeding in equity in the Supreme Court of the District of Columbia against the commission, as defendants, to vacate, set aside, or modify any such decision or order on the ground that the valuation, rate or rates, tolls, charges, schedules, joint rate or rates, or regulation, requirement, act, service or other thing complained of fixed in such order is unlawful, inadequate, or unreasonable. The answer of the commission, on any such action being instituted against it, or the answer of any public utility on any such action being commenced by said commission against it, shall be filed within ten days, whereupon said proceeding shall be at issue’ and stand ready for trial. All such proceedings shall have precedence over any civil cause of a different nature pending in such court, and the Supreme Court of the District of Columbia shall always be deemed open for the trial thereof, and the same shall be tried and determined as are equity proceedings in said court. Any party, including said commission, may appeal from the order or decree of said court to the Court of Appeals of the District of Columbia, and therefrom to the Supreme Court of the United States, which shall thereupon have and take jurisdiction in every such appeal. Pending the decision of said appeal the commission may suspend the decision or order appealed from for such a period as it may deem .fair and reasonable under the circumstances: Provided, That no appeal, unless the court or the commission shall so order, shall operate to stay any order of the commission. .. .” .