What are the 3 heads of Kerberos?

[Sean Krulewitch]

OK, I've heard three different definitions for the "3 heads" of Kerberos,
which is generally accepted?

1. Authentication, Authorization, Accounting were the inital three goals of
Kerberos, however they only delivered on the first, but the name stuck

2. The three heads are the two principals and the KDC (client, server, KDC)

3. The three heads are the AS, TGS, and Kerberos database