A  Class of Entity is a Class of Element that classifies Entitys. Being a subtype of Entity, it is also an instance of itself.

Note:

1)   SysFEAT is a higher-order ontology, so   Class of Entity may have instances that are also  Class of Entity (Class of Classes).

2)   SysFEAT is also a non-well-founded and allows for self-referencing   Class of Entity.

 Mixed-Order Entity is a class of Entitys that is transversal to order levels, defined polymorphically over the universe hierarchy (for every level u).

It is a polymorphic subtype of Entity (declaration: MixedOrderEntity u ⊏⋆ₑ Entity v) and a power instance of Class of Mixed-Order Entity (declaration: ∷ₚₑ), which means that its subtypes may classify entities belonging to any universe level, whereas an Ordered Entity and its subtypes are anchored to a fixed level.

A Mixed-Order Entity has no direct instances: it represents an aspect - a transversal characteristic  - that an ordered class acquires through the aspect relation (⊏ₐₑ) without giving up its level anchoring.

It is the SysFEAT counterpart of MLT*'s orderless type, with two constitutive differences: transversality is carried by the universe polymorphism of the type system (rather than by a FOL axiomatization of integer levels), and cross-level classification goes through the controlled-reflexivity predicates (⊏ₘ, ∷ₘ), which makes it compatible with proof-kernel verification.

Example:

1) Aspects of Entitys, such as Lexical Scope.

2) Building Blocks.

 Ordered Entity is a class whose sub-types are classifed by a Class of Ordered Entity: It is the power instance of Class of Ordered Entity.

Examples:

- First Order Entity

- First Order Class

- Second Order Class