[Lingo] use of でも

[steve smith <sjs@example.com>]

I recently bought a book on writing.  It has the sentence below:

その証拠に、利き手でも反対の手でも、定や口でも書けます。
I think I understand the words but the sentence makes no sense to me. 
What I see is "The proof is, dominant hand ??? other hand ???, 
determine and opening ??? writing."

Can someone tell me what this says?  What is 「でも」saying in this case?

Thanks!
Steve S.