diff --git a/networks.rkt b/networks.rkt
index 83b0b17..86f5668 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -32,6 +32,8 @@
    interaction? get-interaction-sign build-interaction-graph
    build-interaction-graph/form build-signed-interaction-graph
    build-signed-interaction-graph/form
+
+   Modality Mode
    )
 
   (define-type (State a) (VariableMapping a))
@@ -507,6 +509,9 @@
          (define n2 (network-form n-multi 123-doms))
          (check-equal? (graphviz (build-signed-interaction-graph/form n2))
                        "digraph G {\n\tnode0 [label=\"y\"];\n\tnode1 [label=\"t\"];\n\tnode2 [label=\"z\"];\n\tnode3 [label=\"x\"];\n\tsubgraph U {\n\t\tedge [dir=none];\n\t\tnode0 -> node0 [label=\"1\"];\n\t}\n\tsubgraph D {\n\t\tnode0 -> node1 [label=\"0\"];\n\t\tnode0 -> node2 [label=\"-1\"];\n\t\tnode0 -> node3 [label=\"1\"];\n\t}\n}\n")])))
+
+  (define-type Modality (Setof Variable))
+  (define-type Mode (Setof Modality))
   )
 
 (require 'typed)
@@ -665,13 +670,7 @@
 ;;; Dynamics of networks
 ;;; ====================
 
-;;; This section contains definitions for building and analysing the
-;;; dynamics of networks.
-
-;;; A modality is a set of variable.
 (define modality? (set/c variable?))
-
-;;; A mode is a set of modalities.
 (define mode? (set/c modality?))
 
 ;;; A network dynamics is a network plus a mode.
diff --git a/scribblings/networks.scrbl b/scribblings/networks.scrbl
index aa26afb..c903306 100644
--- a/scribblings/networks.scrbl
+++ b/scribblings/networks.scrbl
@@ -362,6 +362,20 @@ values represented as 0 and 1.
 @ex[
 (build-all-01-states '(a b))
 ]}
+
+@deftype[Modality]{
+
+A modality is a set of variables.  This is a synonym of @racket[(Setof
+Variable)].
+
+}
+
+@deftype[Mode]{
+
+A mode is a set of modalities.  This is a synonym of @racket[(Setof Modality)].
+
+}
+
 @section{Inferring interaction graphs}
 
 This section provides inference of both unsigned and signed interaction graphs.