Definition monotone6 T0 T1 T2 T3 T4 T5 (gf: rel6 T0 T1 T2 T3 T4 T5 -> rel6 T0 T1 T2 T3 T4 T5) :=
  forall x0 x1 x2 x3 x4 x5 r r' (IN: gf r x0 x1 x2 x3 x4 x5) (LE: r <6= r'), gf r' x0 x1 x2 x3 x4 x5.

Theorem paco6_acc: forall l r (OBG: forall rr (INC: r <6= rr) (CIH: l <_paco_6= rr), l <_paco_6= paco6 gf rr), l <6= paco6 gf r.