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)

what’s not working?