Definition e := (y0 ++ [#;$]) / [$].
Definition P := [d ; e] ++ R ++ [ ([#] / [#] )] ++ map (fun a => [a] / [a]) Sigma.

Lemma rew_subset u v : u / v el R -> u / v el P.
Fact SR_MPCP x :
x <<= Sigma -> x ≻* y0 -> exists A, A <<= P /\ tau1 A = x ++ [#] ++ tau2 A.