The Grimshaw theme is an interference with two black pieces arriving on a particular square mutually interfere with each other.

It is named after the 19th century problem composer Walter Grimshaw.

Walther Grimshaw (England, 1832-1890)

Special theme's with the same interference idea are Novotny, Plachutta, Plavotny and Nochutta.

Here the cql for Grimshaw studies. You also will find studies with Novotny's and other interference themes because they are specials.

CQL 5.1
; Black moves either a rook or a bishop to an unattacked square not on the edge ; This does not look for interference, so there are false positives cql(input heijden.pgn variations sort matchcount 1 100 result 1-0) mainline square $attacked in b-g2-7 move from r to $attacked move from b to $attacked next(any not attacks (A $attacked))

CQL 3.2

:pgn heijden.pgn
:output Grimshaw.pgn
:moveto ?b2
((position :sequence ( (position :movefrom b :moveto ?b2)))
(position :sequence ( (position :movefrom r :moveto ?b2)))
; Has some false positives

Here a few examples found in the Harold van der Heijden V database 2015