diff --git a/networks-tests.rkt b/networks-tests.rkt
index 9039834..1c847ba 100644
--- a/networks-tests.rkt
+++ b/networks-tests.rkt
@@ -96,3 +96,8 @@
     (check-false (has-edge? sig2 'c 'a))
     (check-equal? (edge-weight sig2 'a 'b) 1)
     (check-equal? (edge-weight sig2 'b 'a) -1)))
+
+(test-case "Dynamics of networks"
+  (let ([vars '(a b c)])
+    (check-equal? (make-asyn vars) (set (set 'a) (set 'b) (set 'c)))
+    (check-equal? (make-syn vars) (set (set 'a 'b 'c)))))
diff --git a/networks.rkt b/networks.rkt
index 590df13..52aab7f 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -30,7 +30,9 @@
                [make-boolean-domains (-> (listof variable?) (hash/c variable? (list/c #f #t)))]
                [get-interaction-sign (-> network-form? domain-mapping/c variable? variable? (or/c '+ '- '0))]
                [build-signed-interaction-graph (-> network-form? domain-mapping/c graph?)]
-               [build-boolean-signed-interaction-graph (-> network-form? graph?)])
+               [build-boolean-signed-interaction-graph (-> network-form? graph?)]
+               [make-asyn (-> (listof variable?) mode?)]
+               [make-syn (-> (listof variable?) mode?)])
  ;; Predicates
  (contract-out [variable? (-> any/c boolean?)]
                [state? (-> any/c boolean?)]
@@ -254,3 +256,12 @@
 
 ;;; A network dynamics is a network plus a mode.
 (struct dynamics (network mode))
+
+;;; Given a list of variables, builds the asynchronous mode (a set of
+;;; singletons).
+(define (make-asyn vars)
+  (for/set ([v vars]) (set v)))
+
+;;; Given a list of variables, builds the synchronous mode (a set
+;;; containing the set of variables).
+(define (make-syn vars) (set (list->set vars)))