Revisiting the half-pin

 
After a hiatus I realized that there are so many more half-pin problems that I want to put on the blog.  In this post I will focus on problems that use a half-pin as a means to achieve something else.

Moen, Kabe
The Problemist Supplement 2016

#2

9 + 7

Notice the half-pin set up on the diagonal d4-h8.  How should white mount a threat? 

Ellerman, Arnoldo
Good Companion 1921

#2

10 + 10

   
This is an absolute masterpiece that deserves careful study.  The key 1.Sd7 threatens 2.Sb6#.  The main thematic pieces are the half-pinned bB and bQ along the fifth rank.  The bQ has two flight granting defenses which are both met by double-pin mates: 1...Qxe6 2.Rxd6# and 1...Qxf3 2.Sxf6#.  The play of the bB is also interesting and known as black correction.  If we were to simply remove the bB from the board this would do two things: defeat the threat of by vacating the square e5 and allow the mate 2.Rxd6 by unguarding d6.  The bB has to land somewhere and if it stays along the e5-g3 diagonal it still guards d6 but commits other errors: 1...Bf4 interferes with bRh4 allowing 2.Qd1#, while 1...Bg3 interferes with bRg8 allowing the Q+P battery to shut-off with 2.f4#.  One more correction move for the bB.  1...Bd4+ unguards d6 but also checks White (which the key granted!) so Rxd6 won't work.  However, it commits another error by self blocking d4 allowing the B+S battery to fire with 2.Sc5#.  All of these mates fully utilized the bQ being pinned.  

Mansfield, Comins
The Chess Amateur 1919

#2

11 + 10

The bP's give this away as a waiting move problem.  Every move of black has a set mate.   We are interested in the play of the bS and bR on the fifth rank.  Any move of bSe5 unguards c4 allowing 2.R(x)c4 while moves of the bR are met with captures 2.Qxd6 and 1...Rd4 2.exd4.    When looking for the key, one thing to notice is that a move by bRd5 will open the wB's guard to c6.  This hints at the key 1.Rf5 setting up the half-pin.  1...Rd4 2.Qxc6 which uses the fact that bSe5 is pinned.  The bS has interesting play: 1...Sf7,Sg6 2.Qe3# and 1...Sf3,Sg4 2.Qd6# both depending on the pinned bR at d5.  But the most interesting variation is 1...Sc4 which defeats both Qd6 and Qe3 but self blocks c4 to give way for another pin-mate 2.Sxd3#.  
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Sheppard, Charles
Good Companion 1921

#2

9 + 8

I had never heard of Charles Sheppard until a recent article of The Problemist.  Here is a nice use of the half-pin to allow an en passant ​capture.  Key: 1.f4 (>2.Qe3#) 1...exf3 ep 2.Sd4#, 1...exf4 2.Qf3.

Sheppard, Charles
Chess Correspondent 1943

#2

10 + 8

Another nice problem.  Here Sheppard uses the half-pin to show the black correction four-way formula: a piece opens a black and white line and simultaneously closes different black and white lines.  The key is 1. Sh5 (>2.Sf4#) and the variations showing the four-way formula are: 1...Sd7 2.Sxc7#, 1...Sf7 2.Sxg7# and 1...Sd3 2.d5#.  

Mansfield, Comins
Hampshire Telegraph and Post 1915

#2

10 + 12

Another one of Mansfield's well known problems.  Here the master of the half-pin uses it to pull of a Goethart unpin.  The key 1.Bc7 threatens the double check 2.Ra5.  The thematic half-pinned bBb4 and bSd4 can defend against the threat.  1...Sxb5 leads to the double pin mate 2.bxa8=Q (this is the purpose of the wasteful wPb7 and bBa8) while the checking 1...Sb3 is met by the capture 2.axb3.  More interesting are the defenses by the bB of which any move defeats the threat by vacating the square b4.  1...Ba3 and 1...Ba5 self block allowing 2.Rb6 and 2.b3 respectively.  While 1...Bc3/Bc5 allow the beautiful Goethart unpin 1...Rb3.  The idea is that b3 is really the only square for the wRb5 to go to but this unpins the bRc2.  However, the bB interferes with the bR along the c-file letting it happen.  One more interference mate: 1...Bd2 2.Qxc2.

Bottacchi, Antonio
L'Italia Scacchistica 1918

#2

7 + 5

Here is another classic and one of only a handful of problems that earns the prestigious masterpiece label in Jeremy Morse's Chess Problems: Tasks and Records book.  This beautiful Meredith uses the half-pin to achieve the record of 4 pin-mates + selfblock.  The initial flight 1...Kc5 is provided with 2.Qb5.  The give and take key 1.Se6 offers the wS for triple sacrifice.  Pure elegance.

Pimenov, Sergej and Umnoff, Evgenij
Western Morning News 1930

#2

7 + 10

Here the composers play a little trick on the solvers.  Notice the half-pin set up along the fourth rank.  Moves by the bSe4 open the gate for 2.Bd5.  The bS can correct, however, and 1...Sc3 self-blocks allowing 2.Sb2 and 1...Sef6 interferes with bB's line for 2.Se5.  There is no mate set for 1...Sd2.  The bSg4 also has some interesting set play: 1...Se5 interferes with the bB allowing 2.Qxe4/Rex4 (this is a hint into the solution) 1...Se3 interferes with the bQ allowing 2.Be2.  And finally 1...Sgf6 succumbs to 2.Se5 (no pin necessary here).  Despite the appearance of a half-pin, there is really only one necessary pin-mate after 1...Sef6.  The key 1.Qg5! abandons this and swaps it for the interference 1...Sef6 2.Qc1 and the other mates are the same as in the set play.