I don't know why it was removed, but if you need that to work you can define
function Base.isless(A::AbstractVector, B::AbstractVector) a, b = length(A), length(B) a == 0 && return b > 0 for i in 1:min(a,b) A[i] != B[i] && return A[i] < B[i] end return a < b end and then your example your work.