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For a group of edges, <b>Source</b> and <b>Target</b> vertices should be
shared by one edge of the group. If <b>Source</b> and <b>Target</b>
-vertices are specified, the elements of the group must be ajacent.
+vertices are specified, the elements of the group must be adjacent.
The source and target groups must contain equal number of edges
and they must form topologically equal structures.
