proposition: Theorem Book_1_12_part2 : forall A, A -> ~~A.
proof: Proof. intros A a f. exact (f a). Defined.
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)