The rule of thumb is "A king on the 6th rank ahead of it's passed pawn always wins, no matter who's turn to move it is." (However, the outer most a- and h-pawns -- the rook pawns -- are excluded from this rule. If the lone king can occupy Ka8 against the a-pawn, or occupy Kh8 against the h-pawn, the game will become a draw because the lone king cannot be flushed out of the corner which prevents promotion.)

In this game, after 68.Kg6 the White king on the 6th rank is ahead of it's passed pawn. Now it's Black's turn to move. No matter which way Black's king moves, the White king will advance on the opposite file and secure control of the promotion square. Thus, 68...Kh8 69.Kf7 or 68...Kf8 69.Kh7 both protect the path of the g-pawn to promotion. After 72.g8=Q, White will use the new queen to easily force checkmate on the lone Black king. The key move to making this sequence happen was 68.Kg6 getting to the 6th rank ahead of the passed pawn.

However, if White had instead erroneously advanced the pawn 68.g6, the game would have been drawn. Play would have gone 68...Kh8 69.g7+ Kg8 70.Kg6 placing the White king behind the blocked pawn, and stalemate has occurred. The general rule of thumb is "advance the passer to the 7th rank with check, your game is a wreck (unless you already control the promotion square with another piece)."

Any chess book which does not explain how the pieces move, capture and how to record the moves on paper is probably too advanced for students learning the basic endgame patterns. IT IS BETTER TO READ A CHESS BOOK THAT IS EASY, COMFORTABLE THAN ONE THAT IS TOO DIFFICULT TO FOLLOW.

I am fond of older books printed in English descriptive notation by informed master writers Fred Reinfeld, Al Horowitz, Frank Marshall/Irving Chernev, Larry Evans, and Harry Golumbek. "Chess Made Simple" by Milton L. Hanauer isn't pretty to look at, but it is chock full of useful information. Read Hanauer after you've read a few Fred Reinfeld books a couple of times. The endgame chapters in older books written in descriptive notation tend to be much more thorough than skinnier, modern books that skimp on the endings. (Endgame theory is stable over the years; it has not changed so rapidly like opening theory does. Yes, computers have found alterations in complex endings, but not the basic forced endings that will never change. Forced endgame patterns are concrete and continue to crop up game after game, year after year, to the benefit of the student that learned them way back when and keeps on winning, or drawing games s/he could have lost.) Modern instructive chess books tend to have half the pages but of a fancier design and much lower editing standards. Modern books for beginners tend to be works of art for visual appeal, whereas older descriptive books devoid of art had to produce quality educational information to train the brain.

Instructional books by Edward Lasker, Emanuel Lasker and Jose R. Capablanca are also challenging but worthwhile for amateurs and professional players alike. Some of their books have been reprinted in algebraic editions. Translator Julius du Mont has a few books written or co-written in descriptive notation that tickled my fancy. World Champion Dr. Max Euwe and American Champion Reuben Fine have both penned a series of more sophisticated books for beginners, intermediates and advanced players. You can't go wrong by reading their meaty books, but it's not the best place to start for a student needing to learn basic king and pawn endings. Teachers must not overwhelm a youngster with an impossible looking text.

Of course, there are many, many, many good chess books and authors out there. These listed above have barely scratched the surface. There are more books written about chess than all other games combined. Unfortunately, some modern books are written more as a marketing gimmick to be bought and sold than as a proven tool of instruction that withstood critical editing by an informed content editor, as opposed to a graphic designer. Before purchasing a recently published chess book, inquire about the chess credentials of the author and the publishing company. I am grateful for some self-published materials, but not so much in chess materials. That being said, some of the best chess books ever written (usually of an advanced nature) were published in recent years with computer assistance.

Many of the highly informative but colorless older books written in descriptive notation are available for a low price through Dover Publications, or try your local used book store. When purchasing used books on-line, I prefer hard covered books when possible and avoid former library books which are often worn out, stained and messy.

Of course, Amazon Reader, Kindle and other e-books has opened a whole new world to book lovers. So much so, that my comments here are rather archaic, but still useful for the poor, thrifty, underprivileged, or imprisoned person who realizes chess is an inexpensive, yet inexhaustible game for the ages -- anytime, any place, anywhere, any language... with the power to make people happy. Personally, I get more enjoyment sitting down at the chessboard with a book prop of the hard cover version of "The King Hunt in Chess" by W.H. Cozens, introduction by Irving Chernev (revised by John Nunn), than clicking a computer mouse or tapping my finger upon a sensitive touch screen, but whatever trips your trigger as long as you're enjoying this great game after your daily chores are done.

Fool's Mate, Descriptive Notation (DN):
1 P-KB3? P-K4
2 P-KN4?? Q-R5 mate!

Fool's Mate, Algebraic Notation (AN):
1.f3? e5
2.g4?? Qh4#

Fool's Mate, Long form Algebraic:
1.f2-f3? e7-e5
2.g2-g4?? Qd8-Qh4#

Note that Figurine Algebraic Notation (FAN) is represented by the graphic shape of the piece itself instead of it's letter. The squares use the same numbers and letters as algebraic notation.

For example, White Kd4 and Pd2 against the lone Black Kd6 is a known forced win for White. The extra space between the king and his pawn can come in handy, providing an extra move and placing the opponent in zugzwang, being compelled to move into a worse position. In a single pawn ending, the superior side is always looking to achieve this same file "empty square on either side of the superior king" configuration (excluding each outer rook file). Knowing this versatile structural forced win position of placing your king an empty square ahead of your passed pawn can save you much time when under time pressure.

It can be quiet dangerous refusing to gain the opposition when the opponent allows it! White could have gained the opposition with 66.Kg6 and chose not to! This would be a bad choice in other positions. However, GM Zhang's 66.Kh6 greatly avoids the possibility of eventually stumbling into a known stalemate position Kf7 and Pg6 against the lone Kh8 trapped in the corner but not in check. This lone king in the corner stalemate pattern must be imprinted into your chess brain!

In fact, switching the K&P around is also a stalemate: Pf7 and Kg6 vs. Kh8 1/2-1/2. Furthermore, a White queen could replace the pawn in either position, and it's stalemate of the lone cornered king! Note that the two superior units (king and pawn or queen) are "a knight's move away" from the lone cornered king. Know this stalemate pattern and keep it in mind before you ever move that pawn because the pawn cannot be moved backward. A red flag should wave in your chess brain before you ever move either unit onto a square "a knight's move away" from the lone cornered king.

In the actual game, GM Zhang wisely uses two moves to gain the opposition with 68.Kg6 (instead of 66.Kg6) with a "safer" (less prone to blunder into stalemate) position. If properly played, both moves win, so it is a matter of preference. There is no faulting GM Zhang's move choice; it's works perfectly in this position. Just be aware that promptly gaining the opposition of kings when allowed to do so is often the proper course in other endgame positions.