# Subtype for UnionAll

Dear all,

I would like to define ab abstract type `T1{T}` as a UnionAll and to be a subtype of an abstract type `T0{T}`. How can I define a type with the `const` syntax as a subtype of an abstract type ? The following does not give the desired outcome :

``````const T1 = expr{T} where {T} <: T0{T}
``````

I could also fo the other way and define `T0{T}` as a UnionAll and define `T1` as a subtype.

``````abstract type T1{T} <: T0{T} end
``````

but Julia throws the `invalid subtyping in definition of T1` error.

How could I go about either defining a UnionAll as a subtype or defining a subtype of a UnionAll ?

Thanks !

``````julia> abstract type T1{T} <: AbstractVector{T} end

julia> typeof(T1)
UnionAll
``````

what’s not working?