Add gg as a synonym for graph-g.

graph.rkt

@@ -29,11 +29,12 @@
   ;; Wrap the opaque graph structure coming from the generic
   ;; graph library.
   (struct graph (g))
+  (define gg graph-g)
 
   (define (has-vertex? g v)
-    (g:has-vertex? (graph-g g) v))
+    (g:has-vertex? (gg g) v))
   (define (has-edge? g u v)
-    (g:has-edge? (graph-g g) u v))
+    (g:has-edge? (gg g) u v))
 
   ;; 2 Graph constructors
   ;; 2.2 Weighted graphs
@@ -42,7 +43,7 @@
 
   ;; 10 Graphviz
   (define (graphviz g #:output [output #f] #:colors [colors #f])
-    (g:graphviz (graph-g g) #:output output #:colors colors)))
+    (g:graphviz (gg g) #:output output #:colors colors)))
 
 
 (require/typed/provide 'graph-wrapper