I have a wordpress blog running for my dad at global-eyes.dk. The domain "wittig.dk" is also purchased and has an A record pointing to the same webserver of global-eyes.dk. I just realized that visiting wittig.dk does not redirect the user to http://www.global-eyes.dk, but just shows the same website. I believe this would give a negative SEO impact because of being a duplicate. I also noticed googling "wittig.dk" gives results with "wittig.dk" and not global-eyes.dk, as if it's a seperate website.
As far as I understand, 301 redirection is the SEO proper way to forward users. How can I make wordpress forward the user from wittig.dk/www.wittig.dk to http://www.global-eyes.dk? I did a bit of reading about redirecting in the function header at php.net, but found it a bit confusing. So please help! :)