Theoreticians describe many elementary tactical methods and typical maneuvers, for example: pins, forks, skewers, batteries, discovered attacks (especially discovered checks), zwischenzugs, deflections, decoys, sacrifices, underminings, overloadings, and interferences. Simple one-move or two-move tactical actions – threats, exchanges of , and double attacks – can be combined into more complicated sequences of tactical maneuvers that are often forced from the point of view of one or both players. A forced variation that involves a sacrifice and usually results in a tangible gain is called a "combination". Brilliant combinations – such as those in the Immortal Game – are considered beautiful and are admired by chess lovers. A common type of chess exercise, aimed at developing players' skills, is a position where a decisive combination is available and the challenge is to find it.