How to prove NP-Completeness

[lightshine]

how do i show that the VERTEX-COVER problem remains NP-complete even when restricted to inputs consisting of graphs such that all vertices have even degree??

[Hnefi]

As with (virtually) all proofs of NP-completeness, you reduce the solution from a known NP-problem. I'm guessing this is homework, so you should be familiar with reduction.

[lightshine]

so far have I allso understood, but I can't get anything good out of it. :(

[Hnefi]

What known problems have you tried reducing from?

[lightshine]

I've tried with the Set Cover which according to my book (algorithm design by tardos and kleinberg) should be wors in polynomial time. And because it is wors it should prove that Vertex Cover is NP-C, the problem comes due to the special case in this question. Don't really know how to prove it in this specific special case. :S I've thought about trying to prove that this special case is the "same" as the regular one, but then when i trie with the special case i cant really seem to get it right. :'(