Cross Checkers

The Good Companions Two Mover defines a cross check as a check in which white replies by interposition - by crossing the line of check.  

Moen, Kabe
StrateGems 2016

#2

9 + 7

Here is one of my personal favorite compositions.  Although this was an earlier problem, it was a great stepping stone for me in terms of complexity.  Notice there are set capture mates for the bQ's moves to c4,d4, and e4.  The wP on d2 is out of play but offers the try: 1.d4? which guards e5 threatening 2.Se7 as well as guarding c5 and closing the bQ's line, hence also threatening 2.Qb3.  However 1...Qe3 defeats this try.  Since this is not the key it is obvious (from the wPd2 and wRh4) that key might give the bK a flight at d4.  Now lets try moving wBc5 which generates the threat 2.Qc5.  Moves along the diagonal c5-f8 are defeated by 1...Bg1.  Moves along the diagonal a7-f2 make a double threat of 2.Qc5/Qc6 but are defeated by 1...Qc4 because of the flight for the bK on d6.  What remains is the ideal key move of 1.Bd4! which only threatens 2.Qc5.  A good key does one of 3 things: grants flights to the bK, sacrifices a piece, and allows Black to check.  This key does all three!  Plus the play is some of my best stuff with cross-checks, self-pins, and self-blocks variations:

1.Bd4! (2.Qc5)
    1...Kxd4+/Kd6+ 2.Bf5
    1...Qd6 2.Qb3
    1...Se6 2.Bc6
    1...Qxd4 2.Qc6
     
   

Anderson, Gerald
Il Secolo, Meredith Ty 1919

#2

5 + 6

Here's a lightweight favorite of mine.  Again a R+B battery is set up but controlled by bBh7.  The key 1.Kd6! moves the wK right into harms way and gives the bK two flight squares.  However checks by the bR interfere with the bB allowing the battery to fire: 1...Rd3+ 2.Bd5 and 1...Rg6+ 2.Be6.  The key also grants two flights and has beautiful by-play: 1...Kb6 2.Bc2, 1...Kb4 2.Kxc6.

Anderson, Gerald
The Observer 1961

#2

13 + 13

Here is a tour de force again by Anderson.  The problem allows  five cross checks and has a flight granting key!  The key 1.Qb6 guards d4 after the threat 2.Se4.  

   1...Sf~+ 2.Se4 (threat)
   1...Sxd6 2.Sd3
   1...Sd4 2.Rf5
   1...exf6+ 2.Sb7
​   1...exd6 2.Rd4

Guidelli, Giorgio
L'Eco degli Scacchi 1916

#2

9 + 10

​Here is a beautiful problem from one of my favorite composers.  Again the wK walks into a barrage of checks from black batteries.  The composer uses the half-pin mechanism and wonderful battery play to handle the checks

1.Kf7! (2.Qb8)
   1...e5+ 2.S7d5
   1...Bg5+/Bg7+/Bh8+ 2.S3f5
   1...Be5+ 2.S7f5
​   1...Bxe7+ 2.Bxf4

Ovchinnikov, Valentin
«64» 1928

#2

10 + 5

Here is a wonderful problem that was selected as one of the top 100 problems in the book A Century of Good Companions Two Movers.  In the set play the bQ can check on b5, e5 and h5 which are met by

   1...Qb5+ 2.Sc6
   1...Qh5 2.Sf7
   1...Qxe5+ 2.Sxe5

However the key unguarded c4 and closes the wRa5's line changing all three of these mates.
 
1.Sc5! (2.Se6)
   1...Qb5+ 2.Sed7
   1...Qh5+ 2.Sg6 
 
Finally 1...Qxe5+ is met by the threat.

Mansfield, Comins
Queensland Chess Association 1919

#2

10 + 9

Even though we have devoted a whole blog post to Mansfield's cross-checkers we have to include this one.  The pinned bS on f3 is preventing any checks from Black.  Surely the key will not unpin this knight...nope, that's exactly what it does and three cross checks follow.  And like so many of Mansfield's problems the key grants a flight to the bK.  Notice the correction play by the newly unpinned bS.

1.Se4! (2.Rc5)
   1...Sf~+ 2.Sf5
   1...Se5+ 2.Sf6
   1...Sxd4+ 2.Sf2

I'll leave it to you to work out the by-play

Gamage, Frederick
Corres. Chess League of America 1937

#2

11 + 11

Finally we end with a masterpiece from Gamage.  The key 1.Bb4 enables Black's Q+B battery to fire at the wK.  What transpires is  a thing of beauty with a full use of the half pin.

1.Bb4
   1...Bxf3+ 2.Qf5
   1...Bc6+ 2.Sc5
   1...Be4+ 2.Se5
   1...Bxe6+/Bc4+/Bxb3+ 2.Sg5

I'll leave to you to work out the other half-pin the variations by  the bBd4.