Mathematical determination in the scope of usage of international treaty or customary law

The aim of this short text is to determine the number of bilateral non-repeatable relations among defined number of subjects. If the number of bilateral contractual relations is known in some branches of international law, it is quite easy to define number of countries which reciprocal relations are only based on customary international law. It seems that the second group is in some international legal areas still dominated by the first one. This can be observed particularly in case of consular functions, which were not regulated in the multilateral Vienna Convention 1963 but are an object of bilateral consular conventions. The number of those is much smaller comparing to bilateral relations regulated without treaty base.