According to the documentation for isless,

If isless(x, y) is defined, then so is isless(y, x) and isequal(x, y), and exactly one of those three yields true.

My understanding is that this should hold for all possible arguments. However, on 1.9.0-beta4 and master,

julia> using OffsetArrays
julia> x = [1,2,3]; y = OffsetVector(x, -1);
julia> (isless(x,y), isless(y,x), isequal(x,y))
(false, false, false)

This is because isequal(x,y) gives false if x and y have different index ranges. This is also inconsistent with cmp,

julia> cmp(x,y)
0

since according to the documentation cmp(x,y) == 0 should imply isequal(x,y).

Would it be a solution to define isless(x,y) and cmp(x,y) for AbstractVector only if firstindex(x) == firstindex(y) and to raise an error otherwise? Or would that be breaking?