# Type Theory¶

Type theory is the study of types.

Types have a cardinality, which is the number of possible values within that type.

## References¶

## Backlinks¶

- Types have a cardinality
- In type theory a type has a cardinality. The cardinality for a given type is the number of possible values. A cardinality can be finite or infinite. A pair of types with the same cardinality will always be isomorphic.

- The void type is called 'never' in TypeScript
- Although TypeScript has a void keyword it's really another word for
`undefined`

for historical reasons - it isn't the void from type theory.

- Although TypeScript has a void keyword it's really another word for
- A type describes a set of possible values
- In type theory, a type describes a set of possible values. This is usually used to declare what is possible to exist within a variable.

- Void is impossible to construct
- In type theory, void is a type with no elements. This means that it is impossible to construct a void type.