It was settled according to the law established by the British authorities when they had mandate from the League of Nations. In 1946 UN stated that the laws (any law in any place) established by the League of Nations remain in force until they will be surpassed by the laws of the legitimate government. "Legitimate giovernment" was never established at the place where now stands the city of Ariel. Therefore (according to UN) the law which governs that territory (Ariel) remain the one of the British mandate. Therefore establishment of the city of Ariel was legal. Get educated ignorant people.
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from the article: Livnat: Actors who boycott West Bank arts center are ignoramuses