"Card Concepts" says Martin D. Kruskal was a Professor of Mathematics at Princeton. (I'm not vouching for the accuracy of Card Concepts, I'm just saying ... )
Harry may well be referring to the Kruskal principle but it didn't sound like it to me, not exactly.
I know of the Kruskal principle as the one where you count down in a deck the value of a card, then you count down again using the card you counted to, and you repeat this until you get as far in the deck as you can go without running out of cards.
The Kruskal principle is that the ending card will usually be the same regardless of the starting card used, as the different possible paths you could have taken tend to converge.
Perhaps this principle has been modified to get the effect HL described, I do not know.