Block Threat

Welcome to 2016!  A problem in which every black move has set mate (or continuation to mate in #3 or more) is called a complete block problem.  To solve the problem one can look for a waiting move that holds all of these mates.  Sometimes this is not possible and the key must change some of the mates.  If the key does not carry a threat then the problem is called a mutate (see the Change Waiters post on 9/18/15).  If the key carries a threat then the problem is called a block threat.  Block threat problems are somewhat rare problems.

Moen, Kabe
The Problemist Supplement 2015

#2

7 + 7

Click on the diagram for the solution.

Shinkman, William A.
Chess Monthly 1885

#2

8 + 8

Here is a great example of a block threat.  The key 1.Qg1 sacrifices the wQ, gives a flight square, and changes the self blocking mate after 1...Be5.  

Nemcek, Milan Sr.
Pravda 1971

#2

6 + 4

In my opinion this is one of the finest block threats ever composed.  The key 1.Se6! gives a flight square and sacrifices the wS.  Black also has the anticipatory line closing defenses 1...Sc5 and 1...Sd6 which are met by beautiful white interference mates 2.S6c7 and 2.S8c7 respectively.

Penrose, Lionel S.
Good Companions 1916

#2

9 + 8

 
Here is another outstanding block threat.  The key 1.Qd2! threatens 2.Qxa5# but unpins the bRf3.  The unpinned bR can now check with 1.Rf1+ which is handled by the newly formed Q+B battery. 

Strydom, Jan
The Problemist Supplement 1996

#2

10 + 12

Here is a modern example of a block threat.  There are set mates for moves of the bS and 1...cxd5.  All of these are destroyed by the key 1.Sf3 which makes a triple threat 2.Se5/Sd2/Rxd4.  However, every possible combination of the threats is enforced by blacks seven moves: combinative separation.  For example, 1...e1=Q is met by only 2.Rxd4 while 1...e1=R is met by 2.Sd2 or 2.Rxd4 and 1...e1=B is met by 2.Rxd4 or 2.Se5.  Finally 1...e1=S allows all three mates.  AUW! The other black moves further separate the threats.

Bwee, Touw Hian
Schach-Echo 1980

#2

7 + 10

Finally we end with a nice try problem.  There are mates set for every black move but there does not seem to be a waiting move that holds the position.  1.Be7? or 1.Bf6? interfere with the wRf7.  Moves by the wRs interfere with the wBd8.  We have a white Grimshaw and a really nice try problem.  What remains is to make a threat 1.Ba5.