In
type theory
In mathematics and theoretical computer science, a type theory is the formal presentation of a specific type system. Type theory is the academic study of type systems.
Some type theories serve as alternatives to set theory as a foundation of ...
, an empty type or absurd type, typically denoted
is a type with no terms. Such a type may be defined as the nullary coproduct (i.e. disjoint sum of no types).
It may also be defined as the polymorphic type
For any type
, the type
is defined as
. As the notation suggests, by the
Curry–Howard correspondence
In programming language theory and proof theory, the Curry–Howard correspondence is the direct relationship between computer programs and mathematical proofs. It is also known as the Curry–Howard isomorphism or equivalence, or the proofs-as-p ...
, a term of type
is a false proposition, and a term of type
is a disproof of proposition P.
A type theory need not contain an empty type. Where it exists, an empty type is not generally unique.
For instance,
is also
uninhabited
The list of uninhabited regions includes a number of places around the globe. The list changes year over year as human beings migrate into formerly uninhabited regions, or migrate out of formerly inhabited regions.
Definitions
The exact def ...
for any inhabited type
.
If a type system contains an empty type, the
bottom type
In type theory, a theory within mathematical logic, the bottom type of a type system is the type that is a subtype of all other types.
Where such a type exists, it is often represented with the up tack (⊥) symbol.
Relation with the empty type ...
must be uninhabited too,
so no distinction is drawn between them and both are denoted
.
References
{{Comp-sci-theory-stub
Type theory
Unknown content