diff --git a/hott/homotopy/join.hlean b/hott/homotopy/join.hlean
index b17b07dcb..f52f1cdc8 100644
--- a/hott/homotopy/join.hlean
+++ b/hott/homotopy/join.hlean
@@ -41,13 +41,13 @@ namespace join
       apply hconcat, apply vconcat, apply hdeg_square, apply elim_glue,
         apply hdeg_square, apply ap_inv, esimp,
       apply hconcat, apply hdeg_square, apply concat, apply idp_con,
-        apply concat, apply ap inverse, apply pushout.elim_glue, apply inv_inv,
+        apply concat, apply ap inverse, apply elim_glue, apply inv_inv,
       apply hinverse, apply hdeg_square, apply ap_id,
     intro x, induction x with b a, induction b, do 2 reflexivity,
       esimp, apply jglue, induction x with b a, induction b, esimp,
       apply eq_pathover, rewrite ap_id,
       apply eq_hconcat, apply concat, apply ap_compose' (susp.elim _ _ _),
-        apply concat, apply ap (ap _) !pushout.elim_glue,
+        apply concat, apply ap (ap _) !elim_glue,
         apply concat, apply ap_inv, 
         apply concat, apply ap inverse !susp.elim_merid,
         apply concat, apply con_inv, apply ap (λ x, x ⬝ _) !inv_inv,
@@ -60,4 +60,58 @@ namespace join
       apply square_of_eq_top, rewrite idp_con, apply !con.right_inv⁻¹,   
   end
 
+  set_option unifier.max_steps 40000
+  protected definition assoc (A B C : Type) :
+    join (join A B) C ≃ join A (join B C) :=
+  begin
+    fapply equiv.MK,
+    { intro x, induction x with ab c, induction ab with a b,
+      exact inl a, exact inr (inl b),
+      induction x with a b, apply jglue, exact inr (inr c),
+      induction x with ab c, induction ab with a b, apply jglue,
+      apply ap inr, apply jglue, induction x with a b, 
+      let H := apdo (jglue a) (jglue b c), esimp at H, esimp,
+      let H' := transpose (square_of_pathover H), esimp at H',
+      rewrite ap_constant at H', apply eq_pathover, 
+      krewrite [elim_glue, ap_constant], esimp,
+      apply square_of_eq, apply concat, rotate 1, exact eq_of_square H',
+      rewrite [con_idp, idp_con],
+    },
+    { intro x, induction x with a bc, exact inl (inl a),
+      induction bc with b c, exact inl (inr b), exact inr c,
+      induction x with b c, apply jglue, esimp,
+      induction x with a bc, induction bc with b c,
+      apply ap inl, apply jglue, apply jglue, induction x with b c,
+      let H := apdo (λ x, jglue x c) (jglue a b), esimp at H, esimp,
+      let H' := transpose (square_of_pathover H), esimp at H',
+      rewrite ap_constant at H', apply eq_pathover,
+      krewrite [elim_glue, ap_constant], esimp,
+      apply square_of_eq, apply concat, exact eq_of_square H',
+      rewrite [con_idp, idp_con],
+    },
+    { intro x, induction x with a bc, reflexivity,
+      induction bc with b c, reflexivity, reflexivity,
+      induction x with b c, esimp, apply eq_pathover,
+      apply hdeg_square, esimp,
+      apply concat, apply ap_compose' (pushout.elim _ _ _),
+      apply concat, apply ap (ap _), apply elim_glue, esimp,
+      apply concat, apply elim_glue, esimp,
+      induction x with a bc, induction bc with b c, esimp,
+      apply eq_pathover, apply hdeg_square, esimp,
+      apply concat, apply ap_compose' (pushout.elim _ _ _),
+      apply concat, apply ap (ap _), krewrite elim_glue, reflexivity,
+      apply inverse, apply concat, apply ap_id,
+      apply inverse, apply concat, apply inverse, 
+      apply ap_compose' (pushout.elim _ _ _), apply elim_glue,
+      esimp, apply eq_pathover, apply hdeg_square,
+      apply concat, apply ap_compose' (pushout.elim _ _ _),
+      apply concat, apply ap (ap _), krewrite elim_glue, reflexivity,
+      apply inverse, apply concat, apply ap_id,
+      apply inverse, apply concat,
+      --apply ap_compose' (pushout.elim _ _ _),
+    },
+  end
+  check elim_glue
+  check pushout.elim
+
 end join