CountZero,
I am not sure I follow. The node said all elements (to include duplicates). If add a duplicate in @FirstArray, then there has to be a duplicate in @SecondArray to be valid (which works). If I add an duplicate element in the second array, the substring will just shift. Can you give me an example of a data set where it will not work? I am not saying there isn't one (I am fairly certain there is), but your logic doesn't match what my tests have shown.

Cheers - L~R

Update: As I was going to bed last night, I figured out when this wouldn't work. If the second array has duplicates that are in the middle of the list (not on either edge).