fact: Definition fnAux (S : State) (f : rNat -> bool) (i : rZ) (n : rNat) := match eqStateRzDec S (rZPlus n) i with | left _ => negb (f n) | right _ => match eqStateRzDec S (rZMinus n) i with | left _ => negb (f n) | right _ => f n end end.