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 gen_Zeqb_ok : forall x y,
Zeq_bool x y = true -> [x] == [y].