diff --git a/src/graph.xsl b/src/graph.xsl
index 387d1830..0a808616 100644
--- a/src/graph.xsl
+++ b/src/graph.xsl
@@ -51,38 +51,6 @@
     use the node QNames for type checks.}
 -->
 
-<!--
-  Retrieve dependenices for @var{$symbol} on the @var{$graph},
-    using the lookup function @var{$lookup} to resolve external
-    subgraphs.
-  @var{$lookup} will be used only if the symbol cannot be
-    found in @var{$graph},
-    in which case the result of @var{$lookup} will used used in a
-    recursive call as the new @var{$graph}.
-
-  From a graph perspective,
-    the dependencies are edges on the @var{$symbol} vertex.
--->
-<function name="graph:dep-lookup" as="element( preproc:sym-dep )?">
-  <param name="symbol" as="element( preproc:sym )" />
-  <param name="graph"  as="element( preproc:sym-deps )" />
-  <param name="lookup" />
-
-  <variable name="deps" as="element( preproc:sym-dep )?"
-            select="$graph/preproc:sym-dep
-                      [ @name = $symbol/@name ]" />
-
-  <sequence select="if ( exists( $deps ) ) then
-                        $deps
-                      else if ( $lookup ) then
-                          graph:dep-lookup( $symbol,
-                                            f:apply( $lookup, $symbol ),
-                                            $lookup )
-                        else
-                          ()" />
-</function>
-
-
 <!--
   Produce a new graph that is the transpose of
     @var{$graph}@mdash{}that is,
@@ -190,4 +158,60 @@
   </preproc:sym-deps>
 </function>
 
+
+<!--
+@menu
+* Package Subgraphs:: Managing package dependencies
+@end menu
+-->
+
+<!--
+  @node Package Subgraphs
+  @subsection Package Subgraphs
+
+  Each package has its own independent dependency graph.
+  These vertices may have @dfn{virtual edges} to other packages'
+    graphs@mdash{}edges that will be formed once combined the
+    referenced graph;
+      these edges are indicated with @code{preproc:sym-ref/@@src}.
+
+  Graph operations are usually performed on single packages,
+    but it is occionally necessary to traverse packages to recurisvely
+    resolve dependencies.
+  @ref{graph:dep-lookup} makes this easy:
+
+  TODO: Generic graph functions.
+-->
+
+<!--
+  Retrieve dependenices for @var{$symbol} on the @var{$graph},
+    using the lookup function @var{$lookup} to resolve external
+    subgraphs.
+  @var{$lookup} will be used only if the symbol cannot be found in
+    @var{$graph},
+    in which case the result of @var{$lookup} will used used in a
+    recursive call as the new @var{$graph}.
+
+  From a graph perspective,
+    the dependencies are edges on the @var{$symbol} vertex.
+-->
+<function name="graph:dep-lookup" as="element( preproc:sym-dep )?">
+  <param name="symbol" as="element( preproc:sym )" />
+  <param name="graph"  as="element( preproc:sym-deps )" />
+  <param name="lookup" />
+
+  <variable name="deps" as="element( preproc:sym-dep )?"
+            select="$graph/preproc:sym-dep
+                      [ @name = $symbol/@name ]" />
+
+  <sequence select="if ( exists( $deps ) ) then
+                        $deps
+                      else if ( $lookup ) then
+                          graph:dep-lookup( $symbol,
+                                            f:apply( $lookup, $symbol ),
+                                            $lookup )
+                        else
+                          ()" />
+</function>
+
 </stylesheet>
diff --git a/test/graph.xspec b/test/graph.xspec
index c5e32163..7c823f00 100644
--- a/test/graph.xspec
+++ b/test/graph.xspec
@@ -28,86 +28,6 @@
              xmlns:foo="http://www.lovullo.com/_junk"
              stylesheet="graph-test.xsl">
 
-  <scenario label="graph:dep-lookup">
-    <scenario label="given a symbol">
-      <scenario label="in the same package">
-        <scenario label="where dependencies exist">
-          <call function="graph:dep-lookup">
-            <param name="symbol"
-                   select="$foo:document/preproc:symtable
-                             /preproc:sym[ @name='local' ]" />
-            <param name="graph"
-                   select="$foo:document/preproc:sym-deps" />
-
-            <param name="lookup" select="()" />
-          </call>
-
-          <expect label="returns local dependencies"
-                  test="$x:result is
-                          $foo:document/preproc:sym-deps/preproc:sym-dep[
-                            @name='local' ]" />
-        </scenario>
-
-
-        <scenario label="with external @src but local deps">
-          <call function="graph:dep-lookup">
-            <param name="symbol"
-                   select="$foo:document/preproc:symtable
-                             /preproc:sym[ @name='external-but-not' ]" />
-            <param name="graph"
-                   select="$foo:document/preproc:sym-deps" />
-
-            <param name="lookup" select="()" />
-          </call>
-
-          <expect label="returns local dependencies"
-                  test="$x:result is
-                          $foo:document/preproc:sym-deps/preproc:sym-dep[
-                            @name='external-but-not' ]" />
-        </scenario>
-
-
-        <scenario label="where dependencies are missing">
-          <call function="graph:dep-lookup">
-            <param name="symbol"
-                   select="$foo:document/preproc:symtable
-                             /preproc:sym[ @name='missing-deps' ]" />
-            <param name="graph"
-                   select="$foo:document/preproc:sym-deps" />
-
-            <param name="lookup" select="()" />
-          </call>
-
-          <expect label="return empty sequence"
-                  test="empty( $x:result )" />
-        </scenario>
-      </scenario>
-
-
-      <scenario label="in a separate package">
-        <variable name="foo:expected-lookup" as="element()">
-          <foo:lookup-ok />
-        </variable>
-
-        <scenario label="where dependencies exist">
-          <call function="graph:dep-lookup">
-            <param name="symbol"
-                   select="$foo:document/preproc:symtable
-                             /preproc:sym[ @name='external' ]" />
-            <param name="graph"
-                   select="$foo:document/preproc:sym-deps" />
-
-            <param name="lookup"
-                   select="foo:lookup( $foo:expected-lookup )" />
-          </call>
-
-          <expect label="returns external dependenices"
-                  test="exists( $x:result/foo:lookup-ok )" />
-        </scenario>
-      </scenario>
-    </scenario>
-  </scenario>
-
 
   <scenario label="graph:reverse on a disconnected DAG">
     <call function="graph:reverse">
@@ -216,5 +136,98 @@
       <expect label="merges vertices and edges of unique vertices"
               select="$foo:graph-vtwo-vthree" />
     </scenario>
+
+
+    <scenario label="given single graph with duplicate vectors">
+      <call function="graph:union">
+        <param name="graphs"
+               select="$foo:graph-with-dupes" />
+      </call>
+
+      <expect label="mergs duplicates"
+              select="$foo:graph-deduped" />
+    </scenario>
+  </scenario>
+
+
+
+  <scenario label="graph:dep-lookup">
+    <scenario label="given a symbol">
+      <scenario label="in the same package">
+        <scenario label="where dependencies exist">
+          <call function="graph:dep-lookup">
+            <param name="symbol"
+                   select="$foo:document/preproc:symtable
+                             /preproc:sym[ @name='local' ]" />
+            <param name="graph"
+                   select="$foo:document/preproc:sym-deps" />
+
+            <param name="lookup" select="()" />
+          </call>
+
+          <expect label="returns local dependencies"
+                  test="$x:result is
+                          $foo:document/preproc:sym-deps/preproc:sym-dep[
+                            @name='local' ]" />
+        </scenario>
+
+
+        <scenario label="with external @src but local deps">
+          <call function="graph:dep-lookup">
+            <param name="symbol"
+                   select="$foo:document/preproc:symtable
+                             /preproc:sym[ @name='external-but-not' ]" />
+            <param name="graph"
+                   select="$foo:document/preproc:sym-deps" />
+
+            <param name="lookup" select="()" />
+          </call>
+
+          <expect label="returns local dependencies"
+                  test="$x:result is
+                          $foo:document/preproc:sym-deps/preproc:sym-dep[
+                            @name='external-but-not' ]" />
+        </scenario>
+
+
+        <scenario label="where dependencies are missing">
+          <call function="graph:dep-lookup">
+            <param name="symbol"
+                   select="$foo:document/preproc:symtable
+                             /preproc:sym[ @name='missing-deps' ]" />
+            <param name="graph"
+                   select="$foo:document/preproc:sym-deps" />
+
+            <param name="lookup" select="()" />
+          </call>
+
+          <expect label="return empty sequence"
+                  test="empty( $x:result )" />
+        </scenario>
+      </scenario>
+
+
+      <scenario label="in a separate package">
+        <variable name="foo:expected-lookup" as="element()">
+          <foo:lookup-ok />
+        </variable>
+
+        <scenario label="where dependencies exist">
+          <call function="graph:dep-lookup">
+            <param name="symbol"
+                   select="$foo:document/preproc:symtable
+                             /preproc:sym[ @name='external' ]" />
+            <param name="graph"
+                   select="$foo:document/preproc:sym-deps" />
+
+            <param name="lookup"
+                   select="foo:lookup( $foo:expected-lookup )" />
+          </call>
+
+          <expect label="returns external dependenices"
+                  test="exists( $x:result/foo:lookup-ok )" />
+        </scenario>
+      </scenario>
+    </scenario>
   </scenario>
 </description>