State X has accepted the jurisdiction of the ICJ in a unilateral declaration pursuant to Article 36(2) of the ICJ's statute. The declaration, however, contains the following provision: "This declaration shall not apply to disputes with regard to matters which are essentially within the domestic jurisdiction of State X as determined by State X." (a) Is this provision valid? (b) In a suit between State X and State Y, may State Y invoke this provision as to matters it considers within its own domestic jurisdiction? Explain.