And working with 8.6 again

src/GeneralRec.v

@@ -822,7 +822,7 @@ Lemma cassociativity1 : forall A B C (f : A -> comp B) (g : B -> comp C) r c,
   match goal with
     | [ H : Bnd _ _ = Bnd _ _ |- _ ] => injection H; clear H; intros; try subst
   end.
-  subst B.
+  try subst B. (* This line expected to fail in Coq 8.4 and succeed in Coq 8.6. *)
   crush.
   inversion H; clear H; crush.
   eauto.
@@ -836,7 +836,7 @@ Lemma cassociativity2 : forall A B C (f : A -> comp B) (g : B -> comp C) r c,
   match goal with
     | [ H : Bnd _ _ = Bnd _ _ |- _ ] => injection H; clear H; intros; try subst
   end.
-  subst A.
+  try subst A. (* Same as above *)
   crush.
   inversion H0; clear H0; crush.
   eauto.

src/Intro.v

@@ -186,7 +186,7 @@ Some readers have asked about the pragmatics of using this tactic library in the
 (** ** Installation and Emacs Set-Up *)
 
 (**
-At the start of the next chapter, I assume that you have installed Coq and Proof General.  The code in this book is tested with Coq versions 8.4pl5 and 8.5beta2.  Though parts may work with other versions, it is expected that the book source will fail to build with _earlier_ versions.
+At the start of the next chapter, I assume that you have installed Coq and Proof General.  The code in this book is tested with Coq versions 8.4pl6, 8.5pl3, and 8.6.  Though parts may work with other versions, it is expected that the book source will fail to build with _earlier_ versions.
 
 %\index{Proof General|(}%To set up your Proof General environment to process the source to the next chapter, a few simple steps are required.