# Counterexamples to the interpretation \`\<:\` means "is a subtype of"

**URL:** <https://discourse.julialang.org/t/counterexamples-to-the-interpretation-means-is-a-subtype-of/57274>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [March 16, 2021, 8:24am UTC](https://discourse.julialang.org/t/counterexamples-to-the-interpretation-means-is-a-subtype-of/57274 "2021-03-16T08:24:42Z")\
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**Author:** ![path-doc](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/path-doc/32/19183_2.png) [@path-doc](https://discourse.julialang.org/u/path-doc)\
**Post date:** [March 16, 2021, 11:10am UTC](https://discourse.julialang.org/t/counterexamples-to-the-interpretation-means-is-a-subtype-of/57274/12 "2021-03-16T11:10:59Z")

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On the present question, I think @DNF is right, it is a question of making the output of subtypes/supertypes more accurate.

Can I please turn your attention to

> [@A precise definition of what it means to be an instance of an abstract type](https://discourse.julialang.org/t/a-precise-definition-of-what-it-means-to-be-an-instance-of-an-abstract-type/57270/5):
>
> I’m not sure what you mean by “value vy of y” in your definition. If it’s saying that y is an abstract type that implements vy in the way that Int64 is a concrete type that implements 1, then that’s impossible because by definition, only concrete types implement. It looks fine if that detail is omitted: in more familiar terms, x isa y if and only if typeof(x) \<: y. Couple things: isconcretetype(aType) can be used to distinguish a concrete type and an abstract type. Ptr is definitely abstract…

Do you agree that `Ptr{Float64}` is not an instance of `Ptr`? Rather, it is a subtype. In which case, the manual needs updating.

Do you agree with that definition?

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