iled by the
original theory. An axiom of the closure is called a theorem of the
original theory. Any axiom is a theorem. A theory is closed when it is
its own closure. Theories are related through theory morphisms. A
theory morphism from source theory to target theory is a type language
morphism that maps source axioms to target theorems. The context of
theories <span style="font-family: arial; font-weight: bold;">Theory</span>
consists of all theories and their morphisms. The context
<span style="font-fami