Hi,

Regardless of my last email, I've now committed a minor change to  
expl3 repository by which all of \let:NN, \glet:NN, \let_new:NN, and  
\glet_new:NN are defined with \def_protected_long_new, and the  
variants are plain old \def_new. (No change, then, to  \let:NN at all.  
Just bringing the others into line.)

The only real change this makes that I'm aware of is that
   \let_new:NN \par \foo
will now complain '\par already defined' rather than 'runaway  
argument'. I think this is sensible since \let:NN itself does allow  
\par.

Let me know if I've missed something :)

Cheers,
Will