text: with. The vast majority of in-copyright books are out-of-print or out-of-commerce, and most 
  are not actively managed by their rightsholders. There is no oﬃcial registry of copyrighted 
  works and their owners, and existing datasets can be incomplete or erroneous.   16 
  
  As a result, there may be no way to license the vast majority of in-copyright books, especially 
  those that have or have had limited commercial value. 
   Put differently, the barrier to using 
  most books is not simply to pay publishers; even if one had signiﬁcant ﬁnancial resources, 
  licensing would not enable access to most works. 
  
  17 
  
  **Permissively licensed works**
  
  There are books that have been permissively licensed in an easily identiﬁable way, such as 
  works placed under Creative Commons (CC) licenses. Such works explicitly allow particular 
  uses of works subject to various responsibilities (e.g., requiring attribution by the user in their 
  follow-on use). 
  
  While such works could be candidates for inclusion in a books data commons, their inclusion 
  depends on whether the license’s terms can be complied with in the context of AI training. 
  For instance, in the context of CC licensed works, there are requirements for proper 
  attribution across all licenses (the CC tools Public Domain Dedication (CC0) and Public 
  Domain Mark (PDM) are not licenses and do not require attribution).   18 