Editing Pure mate (section)

==Definitions==
A pure mate is a checkmate position such that each of the squares in the king's field is guarded, attacked, or blocked in exactly one way, while the king itself is attacked exactly once.<ref name="bcps">{{cite web |last=McDowell |first=Michael |title=Threemovers |website=British Chess Problem Society |url=https://www.theproblemist.org/beginner.pl?type=b_m3}}</ref> In practice, this means that for each of the squares in the king's field, there is exactly one reason why the mated king cannot be moved to that square to escape check.{{efn|According to Hooper and Whyld, the king's field as-such consists {{em|only}} of the squares {{em|adjacent}} to the king, and does not include the square occupied by the king itself: "It is incorrect to include the square on which the king stands as part of the field."{{sfn|Hooper & Whyld|p=201}}  Nevertheless, inspection of the king's field—together with the square on which it stands—is important both to confirm checkmate, and also to investigate whether a pure mate exists.}} Some authors omit the detail that the mated king {{em|itself}} is attacked only once.<ref name="mayhem">{{cite web |last=Jelliss |first=George |title=A Guide to Variant Chess: Chess Problem Terms |year=2002 |url=https://www.mayhematics.com/v/gp.htm}}</ref> In his ''Dictionary of Modern Chess'', Byrne J. Horton provided the following definition:

{{quote|text='''PURE MATE''': A mating problem situation in which every square next to the black King is guarded by a single white man or occupied by a black man.{{sfn|Horton|p=164}} }}

Horton's definition assumes a historical norm in chess problems, in which White is the attacking and mating side, while Black is the mated and losing side. However, the concept of a pure mate is also applicable to positions in which Black is the mating side.

In the ''[[Oxford Companion to Chess]]'', [[David Vincent Hooper|David Hooper]] and [[Kenneth Whyld]] gave a more complex definition, allowing for exceptions in the cases of pins and double check:

{{quote|text='''pure mate''', or clean mate, a checkmate that meets the following criteria: unoccupied squares in the ''king's field'' are attacked once only; pieces that function as ''self-blocks''{{efn|Hooper and Whyld use the term "self-block" to refer to squares in the king's field which are occupied by friendly units of the same color.{{sfn|Hooper & Whyld|p=364}} }} are not under attack unless necessarily pinned; and the mating move is not a double check unless this is necessary to prevent the defender from interposing a man or capturing a checking piece.{{sfn|Hooper & Whyld|pp=326-327}}{{efn|The composer Gady Costeff noted that this definition does not stipulate that squares in the mated king's field occupied by attacking units must be defended or "covered" exactly once, contrary to the spirit of the basic concept of a pure mate. He also noted that several definitions of pure mate have been given which, although they convey the basic concept, can be construed as having imprecise wording and can be read as mutually incompatible definitions.<ref name="Costeff">{{cite web |last=Costeff |first=Gady |title=puremate.cql |url=http://gadycosteff.com/cql/examples/puremate.html}}</ref>}} }}