  Lack described a Quillen model structure on the category GrayCat of
Gray-categories and Gray-functors, for which the weak equivalences are the weak
3-equivalences. In this note, we adapt the technique of Gurski, Johnson, and
Osorno to show the localization of GrayCat at the weak equivalences is
equivalent to the category of algebraic tricategories and pseudo-natural
equivalence classes of weak 3-functors.
