Twinning by exchange of two statical units 3

a) 1.Sh4! zz
1...fxe1B 2.Qg3+ Bxg3#
1...fxe1S 2.Sxg2+ Sxg2#

b) 1.Qb7! zz
1...fxe1B 2.Qb4+ Bxb4#
1...fxe1S 2.Sd3+ Sxd3#

The role of twinned bishop is clear - from g1 it guards b4-f4 line (after fxe1) and from h1 it guards g2. The reason for his exchange with black rook (instead of simple moving) is clear as well, it is necessary to block black pawns that could otherwise advance. Such an exchange in the middle of black camp is very interesting.

a) 1.Ra6! zz
1...Kxc5 2.Qxc4+ Rxc4#
1...S~ 2.Qd4+ Rxd4#
1...Rb~ 2.Sf4+ Rxf4#

b) 1.Rc8! zz
1...Kxc5 2.Qd4+ Rxd4#
1...S~ 2.Sf4+ Rxf4#
1...Rb~ 2.Qxc4+ Rxc4#

Well known Lacny cycle is achieved by means of two pinning moves of bK on c5 and using two flights c5 and e6. Again, moving the bishop in the twinning is a part of a change mechanism (he plays on a3-c5 line in a), while in b) he guards e5). On the other hand, twinned white pawn has no role except blocking the square for black pawn that could otherwise advance.

a) 1.fxg5! th. 2.Qe5+ Bxe5#
1...Rxc3 2.Sxc4+ Rxc4#
1...Sxc3 2.R4b5+ Sxb5#

b) 1.fxg5! th. 2.Qe5+ Bxe5#
1...Rxc3 2.Rxc4+ Rxc4#
1...Sxc3 2.Sb5+ Sxb5#

Two changed white continuations take place after rook defence at c4 and after knight defence at b5. Knights and rooks of both sides play very actively. The moving of black king in the twinning is the key element of change, note the same key move in both positions. And what about twinned white pawn? In a) position he plays no role, in b) he guards b6 as wRb4 leaves b-file after 1...Rxc3. The economy of the rest of the field is not so good.

a) 1.a8R! Rxc8(Bf1) 2.Rh8 (th. 3.Rhxc8 Sxb3#)
2...Rxa8(Rh1)+ or Re8 or Rg8 3.RhxR Sxb3#
2...Rb8 or Rd8 or Rf8 or Rxh8 3.RaxR Sxb3#
2...Rc7 3.dxc7 Sxb3#

b) 1.d7! Rxc8 (1...Ra8? 2.Qxa8! Sxb3(Bf1)#)
2.dxc8R(Ra8) Rb8 3.a8R!! Sxb3(Bf1)#

Here it can be said that both twinned pieces, wB and wQ, are fully used at c8, while standing on b3 they "only" pin bSc2. In a) White uses the fact, that after capture of Bc8 (bishop doesn't make the move, it is transported thanks to Circe rule and it is allowed in this tourney!) it guards e2 from f1 and thus wRh2 can leave for 8th rank. In b), on the other hand, wQa8 can capture bR at a8, preventing by short variation this defence. It is a case on the edge - should such a move be allowed for thematical unit or not? I tend to admit this kind of problems into tourney.