Add provide statement and undirected edges.

network.rkt

@@ -4,6 +4,11 @@
 
 #lang racket
 
+(provide
+ sylvester-nodes
+ sylvester-edges
+ sylvester-undirected-edges)
+
 (require "sylvester.rkt")
 
 (define (sylvester-nodes m)
@@ -18,6 +23,13 @@
    (map (lambda (k) (map (sylvester-color-edge k) (sylvester-nodes m)))
         (range m))))
 
+(define (sylvester-undirected-edges m)
+  (filter
+   (lambda (edge)
+     (> (sylvester-radix-value (first edge))
+        (sylvester-radix-value (second edge))))
+   (sylvester-edges m)))
+
 (define (sylvester-color-edge k)
   (lambda (v) (list v ((skip-sylvester-radix k) v))))