Changes

== The proof for k=l=1 is was wrong so I removed it -- [[User:Tkiraly|Tamás Király]] 17:16, 8 March 2010 (UTC) ==

The proof that I wrote had written earlier for the ''k=l=''1 case in the remarks is was wrong, so I removed it. A node set <math>X \subseteq V\setminus \{s,t\}</math> of in-degree 2 cannot be deleted, because we may want to use both entering edges in the spanning tree.