diff --git a/networks-tests.rkt b/networks-tests.rkt
index 326500d..de40b3d 100644
--- a/networks-tests.rkt
+++ b/networks-tests.rkt
@@ -85,8 +85,8 @@
          [doms (make-boolean-domains '(a b))]
          [sig1 (build-signed-interaction-graph n doms)]
          [sig2 (build-boolean-signed-interaction-graph n)])
-    (check-equal? (get-interaction-sign n doms 'a 'b) '+)
-    (check-equal? (get-interaction-sign n doms 'b 'a) '-)
+    (check-equal? (get-interaction-sign (nn n) doms 'a 'b) '+)
+    (check-equal? (get-interaction-sign (nn n) doms 'b 'a) '-)
 
     (check-true (has-vertex? sig1 'a))
     (check-true (has-vertex? sig1 'b))
diff --git a/networks.rkt b/networks.rkt
index fada109..5415227 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -31,7 +31,7 @@
                [make-same-domains (-> (listof variable?) generic-set? domain-mapping/c)]
                [make-boolean-domains (-> (listof variable?) (hash/c variable? (list/c #f #t)))]
                [build-all-boolean-states (-> (listof variable?) (listof state?))]
-               [get-interaction-sign (-> network-form? domain-mapping/c variable? variable? (or/c '+ '- '0))]
+               [get-interaction-sign (-> network? 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?)]
                [make-asyn (-> (listof variable?) mode?)]
@@ -238,7 +238,7 @@
 (define (build-all-boolean-states vars)
   (build-all-states (make-boolean-domains vars)))
 
-;;; Given two interacting variables of a network form and the domains
+;;; Given two interacting variables of a network and the domains
 ;;; of the variables, returns '+ if the interaction is monotonously
 ;;; increasing, '- if it is monotonously decreasing, and '0 otherwise.
 ;;;
@@ -249,10 +249,9 @@
 ;;; /!\ This function iterates through almost all of the states of the
 ;;; network, so its performance decreases very quickly with network
 ;;; size.
-(define (get-interaction-sign network-form doms x y)
+(define (get-interaction-sign network doms x y)
   (let* ([dom-x (hash-ref doms x)]
          [dom-y (hash-ref doms y)]
-         [network (network-form->network network-form)]
          ;; Replace the domain of x by a dummy singleton.
          [doms-no-x (hash-set doms x '(#f))]
          ;; Build all the states, but as if x were not there: since I
@@ -293,11 +292,12 @@
 ;;; network for every arrow in the unsigned interaction graph, so its
 ;;; performance decreases very quickly with the size of the network.
 (define (build-signed-interaction-graph network-form doms)
-  (let ([ig (build-interaction-graph network-form)])
+  (let ([ig (build-interaction-graph network-form)]
+        [network (network-form->network network-form)])
     (weighted-graph/directed
      (for/list ([e (in-edges ig)])
        (match-let ([(list x y) e])
-         (list (get-interaction-sign network-form doms x y)
+         (list (get-interaction-sign network doms x y)
                x y))))))
 
 ;;; Calls build-signed-interaction-graph with the Boolean domain for