Variable normalise_correct : forall env b t tg, eval_cnf  env (normalise t tg) ->  hold b (eval env b t).
Variable negate_correct : forall env b t tg, eval_cnf env (negate t tg) -> hold b (eNOT b (eval env b t)).
Definition e_rtyp (k: kind) (x : rtyp k) : rtyp k := x.

Lemma hold_eFF : forall k,
hold k (eNOT k (eFF k)).