unfold coherent at 1 in |- *.
intros U R; red in |- *.
intros x y h; elim h; intros z h0; elim h0; intros H' H'0; clear h h0.
exists z; auto.
Qed.

Theorem Strong_confluence :
forall (U : Type) (R : Relation U), Strongly_confluent U R -> Confluent U R.