Maintenance of a minimum spanning forest in a dynamic planar graph

David Eppstein,
Giuseppe F. Italiano,
Roberto Tamassia,
Robert E. Tarjan,
Jeffery R. Westbrook,
and Moti Yung

*J. Algorithms* 15:173, 1993

*Mathematical Reviews* 94b:68039, 1994

The merge operation defined on page 44 is incompletely defined. The merge operation requires that the vertices $u$ and $v$ to be merged belong to different trees. Otherwise the merging can produce a cycle.