proposition: Theorem Book_1_13 : forall P, ~~(P + ~P).
proof: Proof. intros P f. apply Book_1_13_aux in f. destruct f as [np nnp]. exact (nnp np). Qed.
imports: HoTT(Basics Types HProp HSet Projective TruncType Truncations Modalities.Notnot Modalities.Open Modalities.Closed BoundedSearch Equiv.BiInv Spaces.Nat Spaces.Torus.TorusEquivCircles Metatheory.Core Metatheory.FunextVarieties)