%0 Journal Article %T Interaction properties of relational periods %A Tomi K£¿rki %A Tero Harju %A Vesa Halava %J Discrete Mathematics & Theoretical Computer Science %D 2008 %I Discrete Mathematics & Theoretical Computer Science %X We consider relational periods where the relation is a compatibility relation on words induced by a relation on letters. We introduce three types of periods, namely global, external and local relational periods, and we compare their properties by proving variants of the theorem of Fine and Wilf for these periods. %U http://www.dmtcs.org/dmtcs-ojs/index.php/dmtcs/article/view/630