Authorship Attribution: What's Easy and What's Hard?

This paper considers four versions of the authorship attribution problem that are typically encountered in the forensic context and offers algorithmic solutions for each. Part I describes the simple authorship attribution problem described above. Part II considers the long-text verification problem, in which we are asked if two long texts are by the same author. Part III discusses the many-candidates problem, in which we are asked which among thousands of candidate authors is the author of a given text. Finally, Part IV considers the fundamental problem of authorship attribution, in which we are asked if two short texts are by the same author. Although other researchers have considered these problems, here we offer our own solutions to each problem and indicate the degree of accuracy that can be expected in each case under specified conditions.