F. The provisions of this Convention shall not apply to any person with respect to whom there are serious reasons for considering that: (a) He has committed a crime against peace, a war crime, or a crime against humanity, as defined in the international instruments drawn up to make provision in respect of such crimes; (b) He has committed a serious non-political crime outside the country of refuge prior to his admission to that country as a refugee; (c) He has been guilty of acts contrary to the purposes and principles of the United Nations.