  In this note, we provide an explicit non-Quillen equivalence between the
category of precubical sets and Gaucher's category of flows via a class of
"realization functors" (with mild assumptions on the cofibrations of the
category of precubical sets). In addition, we demonstrate a Quillen equivalence
between simplicial semicategories and flows before proving that simplicial
semicategories satisfy many of the same properties as flows. Finally, we
introduce the category of boxed symmetric trees, presheaves on which may
provide a slightly more flexible setting for concurrent computing than
(pre)cubical sets, before showing that when endowed with degeneracies, the
aforementioned presheaf category is a test category (although not strict test).
