(two homosexual women married in Canada at a time when homosexual marriages were legitimate under provincial law; at time of death of first of the two homosexuals, parties lived in NY which recognized such marriages as legal under state law; surviving homosexual claimed marital deduction for estate tax purposes; IRS denied deduction on basis that Defense of Marriage Act (DOMA) (which was passed by overwhelming majorities in both parties in the Congress and in both bodies) did not recognize homosexual marriages for purposes of federal benefits; Obama Administration refused to defend law so law defended by Bipartisan Legal Advisory Group from U.S. House of Representatives; Court held that, for purposes of federal law, portion of DOMA defining marriage in manner consistent with Natural Law as a union between one man and one woman unconstitutional as deprivation of equal liberty guaranteed by Fifth Amendment in absence of specific federal policy; by so holding, Court suggested that the Congress does not have the power to define meaning of words in statutes enacted by the Congress; Court's ruling does not impact portion of DOMA providing that no state is required to give effect to another state's recognition of homosexual marriage; presently 38 states have laws prohibiting homosexual marriage; Court's opinion lays groundwork for all types of consensual adult sexual behaviors to be deemed legal).