I don't get it. What was wrong with the following abbreviations: "Contents of the Address Register" (CAR), "Contents of the Decrement Register" (CDR)? IMO they'

I don't get it. What was wrong with the following abbreviations: "Contents of the Address Register" (CAR), "Contents of the Decrement Register" (CDR)? IMO they're self-describing. It also allow you to use all the premutations of Address and Decrement registers: C[A|D]+R. How do you do this with "first" and "rest"? ;)