Some authors allow that special situations involving double check or pins may also be considered as pure mate.
An economical mate is a position such that all of the attacker's pieces[a] contribute to the checkmate, with the (optional) exception of the king and the pawns.
[9] In his Dictionary of Modern Chess, Byrne J. Horton provided the following definition: 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.
In the Oxford Companion to Chess, David Hooper and Kenneth Whyld gave a more complex definition, allowing for exceptions in the cases of pins and double check: 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[d] 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.
The three squares g1, h2 and g3 were blocked by friendly pieces (referred to by Hooper and Whyld as self-blocks[11]), none of which were also attacked by opposing units.
For this reason, some authors prefer to use the word "guarded" rather than "attacked" to describe such limitations on the king's movement.
In professional chess, when a game is clearly lost, it is customary for the losing player to resign rather than play until checkmate, both out of respect for one's opponent and also to avoid the tedium of forcing the opponent to play until checkmate, which the winning player may view as poor sportsmanship.
The final result was a pure mate, with a black rook, bishop and knight trapping the white king against the edge of the board.
Anderssen allowed a double rook sacrifice in order to develop an attack using his remaining minor pieces.
In chess composition, the aesthetic concept which allows for this expanded definition of pure mate is called economy of force.
[3][20] Economy of force refers to the idea that a chess composition is simpler and more beautiful when it uses minimal material to maximal effect, e.g. in a checkmate or some particular tactic.
But if the minimum force necessary in order to ensure checkmate requires a double check or a pin, then the resulting position may be regarded as a pure mate.
The fact that the position is a double check is necessary in order for it to be a checkmate, and therefore some authors allow it as a pure mate.
If this move is played, Black will be mated in a position involving a pinned piece in the king's field.
The position might be a pure mate, except that a7 is both occupied by a friendly pawn and also attacked by the white queen.
[12] White could instead play 1.Qd5#, simultaneously unpinning the black pawn and delivering a genuine pure mate.