The Half-Pin Theme

The idea behind the half-pin is the following: two black pieces lie on a white line leading to the bK.  If one of them moves, then the other is pinned.  Below are some of my favorite half-pin problems.  Click on the diagrams for a full solution.

#2

5 + 4

Here is an unpublished half-pin of my own.  Have a go at solving it and scroll down for the solution.

Loyd, Samuel
Chess Monthly, 1859

#2

8 + 8

Sam Loyd's famous problem was one of the first half-pins to appear and the first masked half-pin.  The key 1.Qc8! (-) tucks the wQ behind three pieces.  If the bB or bQ move off of the file then Sc7 is free to mate since the remaining piece will be pinned.

Mansfield, Comins
In Tramway (Lo Scacchista), 1921

#2

8 + 8

The genius of the two mover was also a genius of the half-pin theme and in fact coined the name 'half-pin'.  There are so many many great Mansfield half-pins to choose from (1.Bc7!, 1.Qb7!, 1.Pc7!, 1.Sd2! etc.), here we only pick two.  This problem is one of my personal favorite Mansfields.  Here the half-pin is used to perfectly execute the Albino theme - a white pawn in its initial position makes each of its four possible moves.   The threatless key 1.Sb5! (-) introduces eleven variations.

Mansfield, Comins
El Ajedrez Argentino 1926

#2

11 + 10

One of Mansfield's most famous problems.  The key 1.Qe7 places the key piece en prise and gives a flight square to the king which allows a cross check by bBg6.  

Bwee, Touw Hian
Die Schwalbe 1962

#2

6 + 6

Here is a nice Merideth (12-8 pieces) with a half battery and half-pin.  The problem contains a nice try 1.Re5? (1.Qg7#) which has mates for 1...Rg2 2.Sd2# and 1.Rg4 2.Sd4#, but is foiled by 1...Be7!.  The key is 1.Sc5! with the same threat.

The solution to the first problem is 1.Ra4(-).  Once one of the bSs move the bishop can mate on d2 or d6.