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artificial frontier atypical frontier worker coastal frontier coastal frontier defence consumption possibility frontier consumption-possibility frontier cross the frontier customs frontier delivered at frontier delivery at frontier efficient frontier factor price frontier film frontier film franco frontier frontier airport frontier and pioneer life frontier control frontier control point frontier crossing frontier infringement frontier orbitals frontier point frontier regime frontier region frontier station frontier town frontier trade frontier worker geometric frontier internal frontier land frontier last frontier linguistic frontier natural frontier new frontier production frontier curve production possibility frontier production possibility frontier (ppf) sea frontier sea frontier command substitution frontier television without frontier utility-possibility frontier