ZwischenZugZwang!

Reinfeld Position #621
Black to move

The solution to this problem is really neither a Zwischenzug (the 'expected' re-capture isn't delayed, it's never made!), nor is it a proper Zugzwang (Black already has a direct mate-in-1 threat), but it is an amusing if unusual sort of an interference. So I decided to call it ZwischenZugZwang, because it's a bit like both and not quite like a normal interference.

It's readily apparent that 1. ... Kg7 and 1. ... Kh8 fail to 2. Qxe5+, while 1. ... Rf7 gives up the mate threat. If the King steps onto the f-file, then 2. Rf4+ defends, so the answer must be 1. ... Qf7. But how? after 2. Bxf7+ Kxf7 3. Rf4+ again.

We have a mate threat, so the Queen is expendible. 1. ... Qf7 2. Bxf7+ Kf8 ZwischenZugZwang! Hiding behind the enemy Bishop, all the checks are prevented and 3. ... Rh1# is unstoppable.