NIL and DEFCONSTANT [Gall: Bug Report]

["Scott E. Fahlman" <Fahlman@CMU-CS-C.ARPA>]

I agree with Moon that it "is an error" to redefine built-in constants.
It probably is not required that an implementation stop you from doing
this, but it would be a good idea.  

I think that the description on page 56 is OK as it is.  First it says
that there are built-in named constants that you don't get to change.
Here it talks about such things as T and NIL.  Then it says that
"constant symbols defined by Defconstant" are also treated this way, but
that they may be redefined if necessary by using Defconstant again.  I
don't see anything that would imply that T and NIL are implicitly
defined by Defconstant and that they are therefore redefinable.

-- Scott