  The main objective of this paper is to show that the homotopy colimit of a
diagram of quasi-categories and indexed by a small category is a localization
of Lurie's higher Grothendieck construction of the diagram. We thereby
generalize Thomason's classical result which states that the homotopy colimit
of a diagram of categories has the homotopy type of (the classifying space of)
the Grothendieck construction of the diagram of categories.
