End ALMOST_RING.
Variable Rth : ring_theory 0 1 radd rmul rsub ropp req.
Let ARth := Rth_ARth Rsth Reqe Rth.
Add Morphism rsub with signature (req ==> req ==> req) as rsub_ext4.

Lemma Nseqe : sring_eq_ext N.add N.mul (@eq N).
Proof (Eq_s_ext N.add N.mul).