The game of chess is commonly divided into three phases: the opening, middlegame, and endgame. There is a large body of theory regarding how the game should be played in each of these phases, especially the opening and endgame. Those who write about chess theory, who are often but not necessarily also eminent players, are referred to as "theorists" or "theoreticians".
"Opening theory" commonly refers to consensus, broadly represented by current literature on the openings. "Endgame theory" consists of statements regarding specific positions, or positions of a similar type, though there are few universally applicable principles. "Middlegame theory" often refers to maxims or principles applicable to the middlegame. The modern trend, however, is to assign paramount importance to analysis of the specific position at hand rather than to general principles.
Lottery wheeling (also known as lottery system, lottery wheel, lottery wheeling system) is a method of playing lotteries, used by individual players and groups, where you play all possible combinations of a group of numbers. It requires playing more than one ticket and more numbers than those drawn in the lottery. If it's a pick-6 lottery, such as the common 6/49, then a wheeling system can be used to play with 7 or more numbers.
In a pick-6 lottery, an example will be a system with, say, 12 numbers and a guarantee of 4 if 5, meaning that the player will get a 4-win whenever five of his/her 12 numbers are among the six numbers drawn. Players are usually interested to have a certain guarantee in the minimum possible (or minimum known) number of tickets. A lottery wheeling system has a basic guarantee (as in the examples above), but it also has other, secondary guarantees, which can be observed from the table of wins for the system, as in Bluskov's books and .