diff --git a/unify.rkt b/unify.rkt
index 77f3fef..e692d0a 100644
--- a/unify.rkt
+++ b/unify.rkt
@@ -10,6 +10,7 @@
 	 wild
 	 wild?
 	 non-wild?
+	 ground?
 	 variables-in
 	 unify
 	 unify/env
@@ -69,12 +70,24 @@
 (define (variables-in x)
   (let walk ((x x) (acc (set)))
     (cond
-     [(variable? x) (set-add acc x)]
+     [(wild? x) (set-add acc x)]
      [(pair? x) (walk (car x) (walk (cdr x) acc))]
      [(vector? x) (foldl walk acc (vector->list x))]
      [(non-object-struct? x) (walk (struct->vector x #f) acc)]
      [else acc])))
 
+;; Any -> Boolean
+;; True iff the term is completely ground, that is has no variables or
+;; canonical-variables in it.
+(define (ground? x)
+  (let walk ((x x))
+    (cond
+     [(wild? x) #f]
+     [(pair? x) (and (walk (car x)) (walk (cdr x)))]
+     [(vector? x) (andmap walk (vector->list x))]
+     [(non-object-struct? x) (walk (struct->vector x #f))]
+     [else #t])))
+
 ;; Variable Any -> Boolean
 (define (occurs? var val)
   (let walk ((x val))