fact: Definition pin_sn `{Univalence} (n : nat) : Pi n.+1 (psphere n.+1) $<~> abgroup_Z.
imports: Basics Types WildCat Pointed Truncations.Core Truncations.Connectedness Spaces.Int Spaces.Circle Spaces.Spheres Algebra.AbGroups Homotopy.HomotopyGroup Homotopy.HSpaceS1 Homotopy.Hopf