More questions regarding laminate flooring

Firstly, thank you all for answering my last post regarding the brands available in laminate flooring and for your recomendations. I have come to my next headache with regards to laying the stuff down. I have to work around a fireplace and there is very little space beneath the marble bit that juts out form the fire place (you can tell that I'm new to this can't you ;)) is an irregular shape. Do I need to have an expension space between the flooring and this bit? If I do, how do I go about doing it? I'm even wondering if the underlay will go under that bit protruding out of the fire place. BTW it's fixed to the floor with concrete I think. No easy way to lift it off.
Thanks in advance.
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