Positive law by your definition implies legal order, i.e. hierarchical law enforcement under a state, so we can throw that one straight out of the window. Natural law is a bit more tricky. A lot of anarchists reject normative morality as being too easy to use for justifications of hierarchical domination. In addition, from my short skimming over the wikipedia article on natural law, it seems to be born out of an essentialist philosophical approach to human nature which is widely rejected by anarchists. A social constructivist critique would consider the concept as just another construct created by society which has no basis in nature, and that there can be no inherent, objective moral principles that all people can agree to. Anarchism advocates for voluntary association with decentralized institutions, which could mean there could be consensually agreed upon rules within a group or community, but no universally binding rules. I've seen ancaps being fond of natural law but conversely, we don't consider them to be anarchists. FROM https://www.reddit.com/r/Anarchy101/comments/b2ja6c/natural_law_and_anarchy/