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