The study can be considered as a special case of the orthodox chess problem. The goal must be achieved (win or draw, just as in a chess game) without a pre-specified number of moves for the variations.
The study has also unique key and unique solution.
Typically, the studies resemble game-finales (end-games) and they have usually few pieces.
White wins
 | (Problem 84) A. S. Seletsky, First Prize, ”Chess in U.S.S.R.”, 1933 White plays and wins + (5+4) |
| [5q2/s2P1k2/2b5/8/8/3S4/4BK2/6Q1] | |
There are some studies with excellent solutions, they are truly works of art. Such a study is problem-84, by Seletsky, awarded first prize in 1933.
The stipulation white plays and wins forces us to wonder, how much stronger is White?.
White has an excess pawn ready for promotion, but it is already threatened by the black Bishop, the promotion square is guarded by the black Queen, and if the black King moves to capture it, gives discovered check.
The position is much too open and there is no visible way for the white to press the black.
Can you imagine how does White win? Here follows the solution:
Key: 1.Qg5! [d8=Q]
(If 1...Bxd7, then 2.Sf4 and with 3.Bh5+ White wins).
(If 1...Qe7, then 2.d8=Q and White wins).
1...Ke6+ 2.Kg1!!
(We will understand later why this move is noted as excellent, with two exclamation marks).
(It is not good to play 2...Bxd7 3.Bg4+ Kf7 4.Se5+ Ke8 5.Bxd7#)
2...Kxd7 3.Sc5+ Kc8
(It is not good to play 3...Kd6 4.Qg3+ Kd5 5.Bc4+ Kxc4 6.Qb3+ and in the next move the black Queen is lost. If 3...Ke8 4.Bh5+ and Qf8 is lost. If 3...Kc7 / Kd8, then with 4.Se6+ again Qf8 is lost).
4.Ba6+ Kb8
5.Qg3+ Ka8
6.Bb7+ Bxb7
7.Sd7
(The queen Qf8 is under threat and must be moved. A good idea is to give check, but the white King is wisely located on g1 (now the meaning of the second move becomes obvious!) and there is not a safe check from the black. White is also threatening [8.Sb6#] and, if the queen Qf8 leaves row-8, follows mate [8.Qb8#], so...)
7...Qd8
8.Qb8+ Qxb8
9.Sb6#
White, starting from an open position and having a threatened excess pawn, in nine moves, gave with a lonely Knight a smothered mate to black, who got himself cornered.
Let us see a simpler study with similar ending, created by a study-composer with a large production of splendid works. The Russian writer and composer Karl Artur Leonid Kubbel, (06/01/1891 – 18/04/1942), changed his name to Leonid Ivanovich Kubbel after the October 1917 revolution. Leonid had two brothers, Arvid and Evgeny, who were chess-players.
 | (Problem 85) Karl Artur Leonid Kubbel, ”150 Endspielstudien”, 1925 White plays and wins + (3+5) |
| [8/4q3/2p5/2s2Q2/p5S1/7k/8/1K6] | |
Key: 1.Se3+
(Many studies have checking key).
1...Kg3 2.Qg4+ Kf2 3.Qf4+ Ke2 4.Qf1+ Kd2 5.Qd1+ Kc3
6.Qc2+ Kb4 7.Qb2+ Sb3 8.Qa3+! Kxa3 9.Sc2#
The moves of the black were the best, as he tried to save his Queen. It was not enough, because the King was lost.
And now a study were the white wins, avoiding many traps which lead to a draw. The composer of this study is Vladimir Aleksandrowitsh Korol(i)kov, (07/11/1907 – 01/05/1987).
 | (Problem 86) V. A. Korolikov, First Prize, ”Truda”, 1935 White plays and wins + (5+6) |
| [2B5/pR6/2pP1k2/8/6Kb/4p1P1/5p2/8] | |
Key: 1.d7! Ke7
2.Rb8 Bxg3
(not 2... f1=Q 3.d8=Q+ Kxd8 4.Ba6+ Kc7 5.Bxf1 Kxb8 6.gxh4 and white wins)
3.Ra8
(not 3.Kxg3 f1=Q because the previous moves can be repeated now, but the white is without a pawn)
3...f1=Q 4.d8=Q+ Kxd8 5.Ba6+ Bb8
(playing 6.Rxb8 Kc7 leads to a draw)
6.Bxf1 Kc7 7.Ba6 e2 8.Bxe2 Kb7 9.Bf3 Kxa8 10.Bxc6#
[This post in Greek language].
