ly: arial; font-weight: bold;">Theory</span><small
 style="font-family: arial;"><sup>&#8869;</sup></small> is the subcontext
whose morphisms are special &#8211; their bases
have bijective variable functions. Any theory has an initial model,
which is the free model of the base language, restricted to those
tuples satisfying all the axioms of the theory. This model is the
initial model in the collection of all models of that theory. The
initial model passage <span
 style="font-family: arial; font-style: itali