feat(hott/init): add auxiliary definition needed by definitional package

hott/init/default.hlean

@@ -8,6 +8,6 @@ prelude
 import init.datatypes init.reserved_notation init.tactic init.logic
 import init.bool init.num init.priority init.relation init.wf
 import init.types.sigma init.types.prod init.types.empty
-import init.trunc init.path init.equiv
+import init.trunc init.path init.equiv init.util
 import init.axioms.ua init.axioms.funext init.axioms.funext_from_ua
 import init.hedberg

hott/init/util.hlean

@@ -0,0 +1,15 @@
+/-
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+
+Auxiliary definitions used by automation
+-/
+prelude
+import init.trunc
+
+open truncation
+
+definition eq_rec_on_eq {A : Type} {B : A → Type} [h : is_hset A] {a : A} (b : B a) (p : a = a) : eq.rec_on p b = b :=
+eq.rec_on (is_hset.elim (eq.refl a) p) (eq.refl (eq.rec_on (eq.refl a) b))