Backlink with trailing or no traling slash?

http://www.blackhatworld.com/blackh...ks-http-mywebsite-com-http-mywebsite-com.html

[TABLE="width: 199"]
[TR]
[TD]http://www.domain.com/[/TD]
[/TR]
[TR]
[TD]http://www.domain.com[/TD]
[/TR]
[TR]
[TD]http://domain.com[/TD]
[/TR]
[TR]
[TD]http://domain.com/[/TD]
[/TR]
[TR]
[TD]http://domain.com/index.php

If I backlink to all the above URL as anchors is that correct? will it cause duplicate content issue? as I read Google see those URLs as separate URLs instead of one URL.[/TD]
[/TR]
[/TABLE]

This is a very important question and I need an exact answer. And from what I read http://domain.com and http://www.domain.com is different URLs with www and without. Please enlighten me.