started a subdir for the book

book/examples/chapter4/Comment.gf

@@ -0,0 +1,13 @@
+abstract Comment = {
+  flags startcat = Comment ;
+  cat
+    Comment ; Item ; Kind ; Quality ;
+  fun
+    Pred : Item -> Quality -> Comment ;
+    This, That, These, Those : Kind -> Item ;
+    Mod : Quality -> Kind -> Kind ;
+    Wine, Cheese, Fish, Pizza : Kind ;
+    Very : Quality -> Quality ;
+    Fresh, Warm, Italian, 
+      Expensive, Delicious, Boring : Quality ;
+}