The position is a Complete Block as there are set mates for all black moves. There is a good try. Thus this excellent miniature has set play, virtual play and actual play.

Set Play:

1...Be8 2.Qxe8
1...Bf7 2.Qd6	(Self-block)
1...Bg6 2.Qf6	Grimshaw Interferences
1...Rg6 2.Qe8
1...B-elsewhere 2.Qe8
1...Rf6 2.Qxf6
1...R-elsewhere 2.Qf6

Try: 1.Qg7? (for 2.Nc5) Be8!

Key: 1.Kc7! (Waiting move)

Variations:

1...Be8 2.Qxe8
1...Bf7 2.Qd6	(Self-block)
1...Bg6 2.Qf6	Grimshaw Interferences
1...Rg6 2.Qe8
1...B-elsewhere 2.Qe8
1...Rf6; 2.Qxf6
1...R-elsewhere 2.Qf6

As a waiting key move that retained all set mates was available there is no change from set play to actual play. However there is change between virtual and set as well as actual play in one variation:
1.Qg7 Bf7 2.Qe5 as against 1...Bf7 2.Qd6 and 1.Kc7 Bf7 2.Qd6.

Thus the miniature, apart from showing mutual interference between rook and bishop at g6 in both set and actual play, shows a variation with self-block showing change between virtual and actual (and set) play.

Problem 2

Key: 1.Rgg7!
Threat: 2.Ref7

Variations:

1...Rb7 2.Qf3	Grimshaw Interferences
1...Bd5 2.Qxc3
1...Rg5+ 2.Pxg5	Cross-check
1...Rd7 2.Re6

I was thinking that Grimshaw theme involves mutual interference between a rook and a bishop on a particular square (as g6 in Problem 1). While selecting problems for this article, I came across some examples in which the interference was not mutual; there was either a bishop interfering with a rook or a rook interfering with a bishop. My first reaction was that this not Grimshaw interference. Further study revealed that it is not essential for the interference to be mutual to be known as Grimshaw interference. In this problem there is mutual interference between but on different squares. A rook interferes with the bishop on b7 blocking its path to f3 while the bishop on d5 interferes with both the rooks - queen rook's path to e5 and king rook's path to d4. To distinguish such problems from the more common ones showing mutual interference on the same square, the former are called unit Grimshaws.

The problem has an interesting variation with a cross-check. Keys permitting cross-checks are very highly rated. The construction is also interesting with the line-pinned black queen line-pinning the white queen! This gives rise to two interesting mates by the queen.

Another excellent miniature by the composer of Problem 1! I had selected the two problems from different sources and did not realise that they were by the same composer till I started writing the article. As it is an excellent problem, there is no need to change it.

Unlike Problem 1, this is not a complete block, but there are some interesting set mates.

Set Play:

1...Pc5 2.Qd7	}
1...Pc6 2.Qe5		Self-blocks
1...Bc6 2.Qe5

No set mates are provided for other moves of the bishop.

Key: 1.Qc4!
Threat: 1.Qxc7
Variations:

1...Pc5 2.Qe6	Self-block
1...Pc6 2.Qd4	P-Grimshaw
1...Bc6 2.Qb4	and Self-block
1...Bd5 2.Qxd5

The early definition of Grimshaw was interference by a rook or bishop. It has been extended to include mutual interference between a bishop and a pawn. P on c6 interferes with the path of the bishop to d5 to interpose. Similarly the bishop on c6 interferes with the pawn's move to c5 - hence P-Grimshaw.

In this excellent miniature, all the three set mates are changed after the key. All mates in set as well as actual play take advantage of Self-block of squares in the king's field by its own men.

An article featuring Grimshaw theme cannot be considered complete without Sam Loyd's 'Organ Pipes'. Sam Loyd had composed many problems with two rooks and two bishops leading to eight thematic variations showing mutual interference between rooks and bishops on four squares. These have come to be known as 'Organ Pipes'. Other composers too have tried this idea, which later came to be regarded as a theme. No. 4 is the most famous among the 'Organ Pipe' problems.

Key: 1.Qa5!
Threat: None
Variations:
1...Bd7 2.Qd5
1...Rd7 2.Nf5
1...Be6 2.Qe5
1...Re6 2.Nf5
1...Bd6 2.Qd5
1...Rd6 2.Qxb4
1...Be7 2.Qe5
1...Re7 2.Qxb4
1...Bb7 2.Nf5
1...Bf5 2.Nxf5
1...Bc5 2.Qa1 (Self-block)
1...Bg7 or Bh6 2.Qxb4
1...Rd5 2.Qxd5
1...Re5 2.Qxe5