David Bush posed this one as a puzzle on the LG forum, saying:

I believe my opponent was correct to resign in this position, but if the rules were to suddenly change to standard, with link removal allowed and no link crossing, then I would be losing here against best play. Do you see the winning plan for black?

The answer, provided by David Bush, is below the line:

--------------------------

40. S21
41. Q18 42. N21
43. S22 44. V15
45. T16 46. Q20
47. T20 48. T19
49. U18 50. T15

At this point, under PP rules, I could play U15 double linking. But in standard Twixt I would have to remove T16/U18, and then Pierre could play U17 double linking to V15 and T19. -DB

Here's another branch white could take which loses:

40.s21 41.q18 42.n21 43.L19 44.o19 45.p19 46.q20 47.o17 48.k21 49.i21 50.i22 51.k20 52.m20

So, what you're saying is that Black is still losing, technically, but there is at least this subtle blunder that White could have stumbled into.

Under PP rules, black was right to resign. Under standard rules, the final position is a win for black. If white plays the variation I gave, 40.s21 41.q18 42.n21 43.L19 instead of s22, that would lose for white under either ruleset. So under PP rules, white should not take that variation, but play the main line as Alan posted with s22. I included the L19 variation just to show that the solution tree extends along the bottom of the board as well as the right side.

Just to complete my point, the premise of the puzzle is that the rules are standard, not PP. Based on that premise, my L19 branch would not be a blunder by white, because white is lost no matter what he does.