Selections 5

1.Rb6! th. 2.Qd2 th. 3.Se3#, Rxb4#
    2...Rd5 3.Qxd5#
    2...Rd4 3.Qxd4#
1...Qd2 2.Qc3+ Qxc3 3.Rxb4+ Qxb4 4.Se3#
1...Bd2 2.Qc5+ Rxc5 3.Se3+ Bxe3 4.Rxb4#
1...Rd5 2.Rxd5! th. 3.Qd3#, Qd4#, Se5#
    2...Re8+ 3.Re5 th. 4.Qd3#, Qd4#, Qc5#,Rc6#
        3...Qxe3 4.Sxe3#
        3...Rxe5 4.Sxe5#

The key sets up Plachutta threat 2.Qd2! Black defends by moving to the very square d2 as continuation in the threat play would bring wK under fires of checks. Then White exploits mutual interferences of black Q and B. In spite of very string white position the play has to be precise.

1.b7! th. 2.b8S+ Rxb8 3.Rxa5#
1...Rc5 2.S4b5! th. 3.Rxa5#, b8S#, 2...Rbxb5 3.Rxa5+ Rxa5 4.b8S#
    2...Rcxb5 3.b8S+ Rxb8 4.Rxa5#
1...Rd5 2.S6b5! th. 3.Rxa5#, b8S#, 2...Rbxb5 3.Rxa5+ Rxa5 4.b8S#
    2...Rdxb5 3.b8S+ Rxb8 4.Rxa5#
1...Bb4 2.cxb4! th. 3.S4xb5, Rxa5+, b8S+

The short threat introduces two mates that White would continuously threat. Two black defences by Rb5 undo the initially existing interference, but White moves to the square just left by bR (Umnov theme). Choice of arrival square for bR implies the choice of wS for move to b5 - on c5 the rook intereferes with bent line a3-c5-g1, while on d5 it cuts the line g2-c6. Well done!

1.Sb6+?
1...cxb6!

1.Sxf8? th. 2.Sxe6 th. 3.Sxc7#
1...Bxf5!

1.b4! th. 2.b5 ~ 3.b6 ~ 4.b7#, 3...cxb6 4.Sxb6#
1...e5 2.Sb6+ cxb6 3.Bc8 ~ 4.Bb7# (model mate)
1...g6 2.Sxf8 ~ 3.Sxe6 ~ 4.Sxc7#, 3...gxf5 4.Sxc7# (model mate)
1...Bxf5 2.b5 e5 3.b6 Bxd7 4.b7# (model mate)
        3...cxb6 4.Sxb6# (model mate)

Black defends against the very quite threat by preparation of check on the third move: e5-e4-e3+ or g6-Bh6-Bxf4+. But both allow alternative mating attacks and the problem contains altogether four different model mates. Quite non-standard position for Bohemian, I'd say.

1.Qxf6! th. 2.Sxg5+ Rxg5 3.Qh6+ Rh5 4.Qxh5#
1...Sxf6 2.Rb1! th. 3.Bf1#
    2...Bxc6 3.Sd5! th. 4.Sxg5#, Bf1#
    2...Ba6 3.Rb5! th. 4.Sxg5#, Bf1#
1...Bxf6 2.Re1! th. 3.Bf1#
    2...Bxc6 3.Re4! th. 4.Sf4#, Bf1#
    2...Ba6 3.Sc4! th. 4.Sf4#, Bf1#

Excellent study of Novotny interference is opened by sacrificial key. If bS captures, White can count upon mate Sg5#, if bB captures, White can use mate Sf4#. This determines whether White would like to use Rf1 for the interference on b5 or e4.

1.Re2! th. 2.Sg4 th. 3.Bxe5#, 2...Rxe6 3.Sxe3 th. 4.Sc2,Sxf5#
    2...Rf6 3.Bxf6 th. 4.Bxe5#
    2...Rg7 3.Bxg7,Sxe3
1...Bxb3 2.Sd7 th. 3.Bxe5#, 2...Rxe6 3.Sc5 th. 4.Sxe6,Sxb3#
    2...Rf6 3.Bxf6 th. 4.Bxe5#
    2...Rg7 3.Bxg7 th. 4.Bxe5#
1...Bxb5 2.Se8 th. 3.Bxe5#, 2...Rxe6 3.Sxc7 th. 4.Sxe6,Sxb5#
    2...Rf6 3.Bxf6 th. 4.Bxe5#
    2...Rg7 3.Bxg7 th. 4.Bxe5#
1...Rxe2 2.Sh5 th. 3.Bxe5#, 2...Rxe6 3.Sf4 th. 4.Sxe6,Sxe2#
    2...Rf6 3.Bxf6 th. 4.Bxe5#
    2...Rg7 3.Bxg7,Sxg7
1...Rxf3 2.Sh7 th. 3.Bxe5#, 2...Rxe6 3.Sg5 th. 4.Sxe6,Sxf3#
    2...Rf6 3.Bxf6 th. 4.Bxe5#
    2...Rg7 3.Bxg7 th. 4.Bxe5#
1...Rg5 2.Sh7 th. 3.Bxe5#, 2...Rg7 3.Bxg7 th. 4.Bxe5#
    2...f4 3.Sxg5 th. 4.Bxe5#
(1...f4 2.Bxg6 th. 3.Sf~)

After the key any move of Sf6 would mean threat 3.Bxe5#. Interferences of Bh8 by Rg6 do not help much, but capture of Re6 could neutralize the threat. That is why White must choose very precisely the arrival square for the knight. The idea is to have a possibility of lethal fork with double threat. While in the main threat White attacks c2 and f5, in four main variations takes advantage of annihilation of blocking white pieces - Re6 and one other. Good four-move strategy.

1.Ba2! th. 2.Se1+ Kd4 3.Rxd3+ Sxd3 4.Sc2#
1...Qb5 2.Sg5+ Kd4 3.Qe4+ Rxe4, Bxe4 4.Sf3#, Se6#
1...Qg6 2.Se5+ Kd4 3.Sc6+ Rxc6, Bxc6 4.Qd5#, Bxc5#
1...Rxd2,Rxf2 2.Qe1+ Re2 3.Qxe2+ dxe2 4.Re3#

White Siers battery with queen as a rear piece is used in a less usual way. In two main variations after bQ defences the battery fires in a way allowing White to use Novotny interference in the third move. White knight and queen exchange the roles in two Novotnys: they either do the move into the intersection, or make one of final mating moves.

1...dxc5 a 2.Bxe3+ A Kxe5 3.Rxc5+ Kf6 4.Bg5#
1...dxe5 b 2.Bxe1+ B Sd2 3.Rxd2+ exd2 4.e4#

1.Re4! th. 2.cxd6,Qd4+
1...dxc5 a 2.Bxe1+ B Sd2 3.Rxe3! th. 4.Rxd2,Qe4#, 3...c4 4.Qb5#
1...dxe5 b 2.Bxe3+ A Sd2,Bd2 3.Qd7+ Kxe4 4.Qd3#

Although the comparison of positions before and after the key, considering two defences by Pd6, hint at the symmetry between set play and real variations, the opposite is the truth. Reciprocal change is shown in a way avoiding any symmetry, in an almost unbelievable fashion.

1...Bxe4 a 2.Sg5+ A Kd4 3.Se6+ Rxe6 4.Qa7#
1...Rxe4 b 2.Se5+ B Kd4 3.Sc6+ Bxc6 4.Qa7#

1.Qh1! th. 2.Sg1+ Kd4 3.Qf3! th. 4.Qe3,Qxc3#, 3...Sd3+,Sbd1/Scd1,Sd5 4.Q(x)d3/Sxe2#
1...Bxe4 a 2.Se5+ B Kd4 3.Qxe4+ Sxe4 4.Sc6#
1...Rxe4 b 2.Sg5+ A Kd4 3.Qxe4+ Sxe4,Bxe4 4.Se6#

Another reciprocal change. This one is based on different positions of wQ between set play and solution, and the strategy is also changed.

In the set play black selfpin defence by Bb7 and Re7 leave the 7th rank, that is why White forces by use of Siers battery departures of the other black line mover too, so that wQ can mate from a7.

In the solution wQ liquidates black piece on e4 (that is no longer pinned after 2...Kd4) so that white knight from Siers battery could checkmate in delayed fashion.