proposition: Lemma dn (xm : XM) : forall P, ~ ~ P -> P.
proof: Proof. move => P HP. case: (xm P); tauto. Qed.
imports: mathcomp.ssreflect.ssreflect mathcomp(all_ssreflect) CompDecModal.libs(edone bcase fset base modular_hilbert) CompDecModal.CTL(CTL_def hilbert)