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-rw-r--r--lib/stdlib/doc/src/digraph.xml4
1 files changed, 4 insertions, 0 deletions
diff --git a/lib/stdlib/doc/src/digraph.xml b/lib/stdlib/doc/src/digraph.xml
index 5332d7aba5..db96beed6c 100644
--- a/lib/stdlib/doc/src/digraph.xml
+++ b/lib/stdlib/doc/src/digraph.xml
@@ -170,6 +170,10 @@
<p>If the edge would create a cycle in
an <seealso marker="#acyclic_digraph">acyclic digraph</seealso>,
<c>{error,&nbsp;{bad_edge,&nbsp;<anno>Path</anno>}}</c> is returned.
+ If <c><anno>G</anno></c> already has an edge with value
+ <c><anno>E</anno></c> connecting a different pair of vertices,
+ <c>{error,&nbsp;{bad_edge,&nbsp;[<anno>V1</anno>,&nbsp;<anno>V2</anno>]}}</c>
+ is returned.
If either of <c><anno>V1</anno></c> or <c><anno>V2</anno></c> is not
a vertex of digraph <c><anno>G</anno></c>,
<c>{error,&nbsp;{bad_vertex,&nbsp;</c><anno>V</anno><c>}}</c> is