fact: Definition Book_2_1_concatenation3 : forall {A : Type} {x y z : A}, x = y -> y = z -> x = z.
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)