feat(hott): add wedge sum of pointed types, neutrality of wedging with the unit type

hott/homotopy/wedge.hlean

@@ -0,0 +1,35 @@
+/-
+Copyright (c) 2016 Jakob von Raumer. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jakob von Raumer
+
+The Wedge Sum of Two Pointed Types
+-/
+import hit.pointed_pushout
+
+open eq pushout pointed Pointed
+
+namespace wedge
+  section
+  variables (A B : Type*)
+
+  definition Wedge : Type* := Pushout (pconst Unit A) (pconst Unit B)
+
+  -- TODO maybe find a cleaner proof
+  protected definition unit : A ≃* Wedge Unit A :=
+  begin
+    fconstructor,
+    { fapply pmap.mk, intro a, apply pinr a, apply respect_pt },
+    { fapply is_equiv.adjointify, intro x, fapply pushout.elim_on x, 
+      exact λ x, Point A, exact id, intro u, reflexivity, 
+      intro x, fapply pushout.rec_on x, intro u, cases u, esimp, apply (glue unit.star)⁻¹, 
+      intro a, reflexivity,
+      intro u, cases u, esimp, apply eq_pathover,
+      refine _ ⬝hp !ap_id⁻¹, fapply eq_hconcat, apply ap_compose inr, 
+      krewrite elim_glue, fapply eq_hconcat, apply ap_idp, apply square_of_eq, 
+      apply con.left_inv, 
+      intro a, reflexivity },
+  end
+
+  end
+end wedge