fact: Definition contraction_code {y0 : Y} (q00 : Q x0 y0) (pr : { p : P & left x0 = p }) (c : code pr.1 pr.2) : center_code pr.1 pr.2 = c.
imports: HoTT.Basics HoTT.Types Colimits.Pushout Colimits.SpanPushout Homotopy.Join.Core Truncations