# The definition of free type variable

**URL:** <https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575>\
**Category:** General Usage\
**Tags:** question\
**Created:** [November 1, 2019, 5:34am UTC](https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575 "2019-11-01T05:34:12Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![alligatorme](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/alligatorme/32/6962_2.png) [@alligatorme](https://discourse.julialang.org/u/alligatorme)\
**Post date:** [November 1, 2019, 5:34am UTC](https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575/1 "2019-11-01T05:34:12Z")

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In v1.2 manual, the free type varialbe is defined as “We say that a variable V is free in type  
T if T does not contain the UnionAll that introduces variable V.” But in the context, it seems to be “does” instead of “does not”. Is that right?

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**Author:** ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)\
**Post date:** [November 1, 2019, 5:58am UTC](https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575/2 "2019-11-01T05:58:56Z")

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reference for anyone reading this, [More about types · The Julia Language](https://docs.julialang.org/en/v1/devdocs/types/#Free-variables-1)

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [November 1, 2019, 6:25am UTC](https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575/3 "2019-11-01T06:25:01Z")

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I think the wording in the manual is correct. If not used in a `UnionAll`, the variable remains free.

Look at the examples in the manual.

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**Author:** ![alligatorme](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/alligatorme/32/6962_2.png) [@alligatorme](https://discourse.julialang.org/u/alligatorme)\
**Post date:** [November 1, 2019, 1:39pm UTC](https://discourse.julialang.org/t/the-definition-of-free-type-variable/30575/4 "2019-11-01T13:39:10Z")

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![Untitled](https://global.discourse-cdn.com/julialang/original/3X/2/5/2500a07eec03d0bd6514bf4136dfed3e894ac3c4.png)  
It is the sample following the definition. But it seems not match. Or the sample is not correct?