It shall be the duty of the Council, in accordance with the provisions of Article 11, to take under consideration any complaint as to infraction of the above undertakings which is made to it by one or more of the parties to the dispute. Should the Council be of opinion that the complaint requires investigation, it shall, if it deems it expedient, arrange for inquiries and investigations in one or more of the countries concerned. Such inquiries and investigations shall be carried out with the utmost possible dispatch and the Members of the League undertake to afford every facility for carrying them out. {276} The sole object of measures taken by the Council as above provided is to facilitate the pacific settlement of disputes and they shall in no way prejudge the actual settlement. If the result of such inquiries and investigations is to establish an infraction of the above undertakings, it shall be the duty of the Council to summon the Member or Members of the League guilty of the infraction to put an end thereto. Should any Member of the League in question fail to comply with such summons, the Council shall declare it to be guilty of a violation of the Covenant, and shall recommend measures to be taken with a view to end as soon as possible a situation of a nature to threaten the peace of the world. For the purposes of this Article decisions of the Council may be taken by a two-thirds majority. Article 15c. [Sidenote: Article 9 of the Protocol, slightly changed.] The existence of demilitarised zones being calculated to prevent aggression and to facilitate a definite finding of the nature provided for in Article 15d, the establishment of such zones between States mutually consenting thereto is to recommend as a means of preserving peace. The demilitarised zones already existing under the terms of certain treaties or conventions, or which may be established in future between States mutually consenting thereto, may at the request and at the expense of one or more of the conterminous States, be placed under a temporary or permanent system of supervision to be organised by the Council. Article 15d. [Sidenote: Article 10 of the Protocol, with verbal changes.] Any Member of the League which resorts to war in violation of the undertakings contained in the Covenant is an aggressor. Violation of the rules laid down for a demilitarised zone shall be held equivalent to resort to war. In the event of hostilities having broken out, any Member of the League shall be presumed to be an aggressor (unless a decision of the Council, which must be taken unanimously, shall otherwise declare) which (a) has refused to submit the dispute to the procedure of pacific settlement provided by the Covenant, or (b) has refused to comply with a judicial sentence or arbitral award or with a unanimous recommendation of the Council, or