,@ ,. .,

[jonl at MIT-MC (Jon L White)]

When before the last element of a list there is no
structural difference in the resultant data frob, but
for the purposes of GRINDEFing, the first two will be
"recognized", wheras the last form has the flaw that
the READMACROINVERSE feature of GRINDEF wont recognize
it.  Also, in the future, there may be an attempt for 
,@  to actually copy the top level of the list which
it preceeds; in that case,  "(A ,@B)" would produce
a strictly-private list, whereas "(A ,.B)" would
share the cdr with B.