Definition monotone0 (gf: rel0 -> rel0) :=
  forall r r' (IN: gf r) (LE: r <0= r'), gf r'.

Theorem paco0_acc: forall l r (OBG: forall rr (INC: r <0= rr) (CIH: l <_paco_0= rr), l <_paco_0= paco0 gf rr), l <0= paco0 gf r.