destruct (in_dec Literal_eqdec (LNeg p) l).
right;eauto.
contradiction.
destruct (in_dec Literal_eqdec (LNeg p) l);contradiction.
contradiction.
left;assumption.
Qed.

(* Specifications: *)
Theorem Clause_valid : forall l, Valid (ClausetoPropF l) -> Valid_Clause l.
intros;apply Validated_valid;apply TrueQ_impl_Validates;apply H;intros ? Q;destruct Q.