Strange Lookup Configuration

[DavePearce]

The following seems somewhat non-sensical to me:

(module m1)
(defcolumns X Y Z)
(definterleaved (A) (X Y))
(deflookup l1 (X Y) (A Z))

Here, column A has a length multiplier of 2 whilst Z has a multiplier of 1. Therefore, it seems odd to me that we can pair them together for a lookup in this way.

[powerslider]

@DavePearce this lookup can make sense, but I don't think we have lookups of this kind anywhere.
cc: @OlivierBBB