Monday, July 12, 2021

Lead against a confident slam

This is a hand from the PanIIT inter IIT bridge tournament conducted online in 2020/2021. 


Both vul, IMPS. You hold 8x, A9x, Q7xxxx, K9.

Partner passes, RHO opens 1S, you pass. LHO bids 4NT, RHO shows two keycards without Q and LHO bids 6S.


What would you lead?


Given that you hold HA, DQ and CK and LHO jumped directly to 4NT, it is very likely they have a distributional hand with a long and good club suit. The club finesse declarer needs is working, even if they can only take it once.

At the table I tried the lead of C9 from K9. This turned out to be a lucky lead as you can see from the four hands below.


IMPS 
Both 
 North
♠ AQ7
♥ J
♦ K
♣ AQJ76532
 West
♠ 84
♥ A92
♦ Q76532
♣ K9

      


 East
♠ T62
♥ K87643
♦ T98
♣ 4
 South
♠ KJ953
♥ QT5
♦ AJ4
♣ T8

W N E S
P1S
P4NTP5H
P6SPP
P

Declarer decide to spurn the club finesse and went up with the CA and could no longer make the contract!

Monday, July 5, 2021

Cover the plane with strips

 In the 2D plane, a strip is the space between (and including) two parallel lines (which extend to infinity in both directions). The width of a strip is the distance between the two parallel lines that make up a strip. The width of a strip is non-zero (otherwise we just call it a line).


Can you fully cover the 2D plane with strips the sums of whose widths is finite? (Proof required of course).



Scroll down for a solution.



Consider a circle of radius $R$. A strip of width $w_i$ can cover an area at most $2w_iR$.


So strips of total width $w$ (infinite number of strips or not), can cover at most an area of $2wR$.


For sufficiently large $R$, $\pi R^2 \gt 2wR$. So we cannot cover the plane with strips the sum of widths of which is finite.