It is my understanding that public IP blocks are assigned from IANA, which assigns sub-blocks to RIRs, which assigns sub-blocks to ISPs, which assigns sub-blocks to individual ASs as outlined in this question: How are IP addresses actually assigned?
This (and resources like this page) seems to imply a mapping of 1 public IP to 1 AS.
However, anycast seems to work by advertising the same public ip address from multiple locations, providing different paths to that IP. For example:
If public ips are supposed to resolve to a single AS, how does anycast work?