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1. The Convention does not affect any other international instrument to which Contracting States are Parties and which contains provisions on matters governed by this Convention, unless a contrary declaration is made by the States Parties to such instrument.
2. This Convention does not affect the possibility for one or more Contracting States to conclude agreements which contain, in respect of adults habitually resident in any of the States Parties to such agreements, provisions on matters governed by this Convention.
3. Agreements to be concluded by one or more Contracting States on matters within the scope of this Convention do not affect, in the relationship of such States with other Contracting States, the application of the provisions of this Convention.
4. The preceding paragraphs also apply to uniform laws based on special ties of a regional or other nature between the States concerned.